| 2TG Event AS | Wholesale & retail | 2024 |
| 3.M Eiendom AS | Real estate | 2019 |
| 3BH Invest AS | Hospitality | 2023 |
| 3FJELL AS | | 2025 |
| 5 X H Mote National AS | Wholesale & retail | 2002 |
| A Brandth AS | Wholesale & retail | 1977 |
| Abel Invest AS | Wholesale & retail | 2010 |
| Aci Frisør AS | Other services | 2013 |
| Acres Wild AS | Real estate | 2021 |
| Acw AS | Real estate | 2021 |
| Advokatbygg Sjøgata AS | Real estate | 2016 |
| Advokatfirmaet Braut AS | Professional & scientific | 2022 |
| Advokatfirmaet Bredesen AS | Professional & scientific | 2019 |
| Advokatfirmaet Wulff AS | Professional & scientific | 2012 |
| Aini Holding AS | Health & social care | 2021 |
| Aira Invest AS | | 2026 |
| Ak Petrus AS | Real estate | 2005 |
| Akantus Mosjøen AS | Manufacturing | 1997 |
| Aktiv Hjemmehjelp AS | Health & social care | 2019 |
| Albatross Invest AS | Real estate | 1999 |
| Albert Nilsskog AS | Transport & logistics | 2013 |
| Alcoa Norway AS | Manufacturing | 2022 |
| Aleksander Nordaas AS | Information & communication | 2017 |
| Alfgilroy Invest AS | | 2023 |
| Alfheimsgata 28 AS | Real estate | 2023 |
| Alumatiq AS | Information & communication | 2020 |
| Amore Mat Og Vinhus AS | Hospitality | 2015 |
| Amp Bemanning AS | Administrative & support | 2017 |
| Amrod AS | Professional & scientific | 2007 |
| Andelslaget Ungdomslokalet Mosjøen Ba | Other services | 1992 |
| Angermo Invest AS | | 2016 |
| Anleggsgartner 1 Vesterbekkmo AS | Administrative & support | 2011 |
| Aptive-Solutions AS | Professional & scientific | 2026 |
| Arastein AS | Professional & scientific | 2008 |
| Arctic Cooling-Systems AS | Professional & scientific | 2018 |
| Arctic Supply AS | Manufacturing | 2012 |
| Arkitekter I Nord AS | Professional & scientific | 2023 |
| Arn Holding AS | | 2005 |
| Arnt Bilservice AS | Other services | 2016 |
| Art Frisørsalong AS | Other services | 2010 |
| AS Helibygg | Real estate | 1988 |
| AS Nordlandsfly | Transport & logistics | 1985 |
| Aseeo AS | Information & communication | 2021 |
| Asia Food 2 AS | Wholesale & retail | 2018 |
| Askeladden Barnehage AS | Education | 1992 |
| Aspnes Camping AS | Hospitality | 2018 |
| Aspåsen Invest AS | Real estate | 2014 |
| Aten AS | Real estate | 2022 |
| Aufles Holding AS | | 2022 |
| Auto 90 Ans | Other services | 1990 |
| Auto-Odd AS | Other services | 2017 |
| Autonext AS | Wholesale & retail | 2013 |
| Autopro Mosjøen AS | Other services | 1995 |
| Autoservice Mosjøen AS | Other services | 2014 |
| B-Nom Eiendom AS | Real estate | 2007 |
| Bakgården AS | Real estate | 2008 |
| Bakgården Kultur AS | Real estate | 2023 |
| Bardin AS | Real estate | 2004 |
| Barth AS | Wholesale & retail | 2008 |
| Barthbryggo AS | Hospitality | 2023 |
| Bedriftspartner AS | Professional & scientific | 1997 |
| Bedriftspartner Brønnøy AS | Professional & scientific | 2016 |
| Bergsnev Samdrift Da | Agriculture & fishing | 1999 |
| Beste Totalbygg AS | Construction | 2022 |
| Beta Eiendom AS | Real estate | 1997 |
| Betongpumping Mosjøen AS | Construction | 2019 |
| Beverlinjen AS | Administrative & support | 2013 |
| Bilfokus AS | Wholesale & retail | 2009 |
| Bilutleie Mosjøen AS | Administrative & support | 1998 |
| Bio Miljø AS | Water & waste | 1998 |
| Birkeland Mo Invest AS | Financial services | 2017 |
| Bjønnhåjen Samdrift Da | Agriculture & fishing | 2006 |
| Bjørgs Helsesalong AS | Other services | 2009 |
| Bjørnar Kvalfors Ans | Transport & logistics | 1989 |
| Blåfjell Hundesenter AS | Agriculture & fishing | 2019 |
| BMC Trafikkskole AS | Education | 2011 |
| Bodø Properties AS | Real estate | 2017 |
| Boligspesialisten AS | Construction | 2004 |
| Boligspesialisten Bygg AS | Construction | 2013 |
| Boligspesialisten Eiendom AS | Real estate | 2025 |
| Boligvekst AS | Real estate | 2005 |
| Brandth Holding AS | Real estate | 2005 |
| Bratbakk AS | Real estate | 2019 |
| Bratbakk Drift AS | Real estate | 2023 |
| Braut Eiendom Mosjøen AS | Real estate | 2022 |
| Bredesen Sykkelservice AS | Wholesale & retail | 2011 |
| Brillehuset Mosjøen AS | Wholesale & retail | 1998 |
| Britt-Nina's AS | Wholesale & retail | 2005 |
| Brodtkorb AS | Arts & recreation | 2001 |
| Brodtkorb Consulting AS | Professional & scientific | 2019 |
| Brodtkorb Eiendom AS | Real estate | 1999 |
| Brubakk Eiendom AS | Real estate | 1993 |
| Brugata 11 AS | Real estate | 2021 |
| Brugata 13 Eiendom AS | Real estate | 2016 |
| Brugata 9A. AS | Real estate | 2021 |
| Brækken Maskin & Transport AS | Construction | 2001 |
| Brødrene Skjervstad AS | Construction | 1986 |
| Brødrene Skjervstad Holding AS | | 2022 |
| Brønnøy Brygge AS | Real estate | 1973 |
| BS Solhaug AS | Real estate | 2005 |