He played youth football for FK Vidar[1] and Viking FK, being drafted into Viking's senior team in 1994 alongside four other players: Trond Kindervåg, Bjarte Lunde Aarsheim, Erik Fuglestad and Trond Debes.
[6] He was the best Lillestrøm player in a lactate test performed by Olympiatoppen in [7] He could play central or left midfielder, competing with Runar Normann and Leif Gunnar Smerud.
[8] Following a knee injury just before the start of the 1998 Eliteserien, Bjørnsen had to wait until July 1998 to make his Lillestrøm debut.
Already in January, he was told that he was not considered as a starting player, with Runar Kristinsson and Magnus Kihlberg occupying central midfield.
He was allowed to start in the cup, where he scored twice; in the second round, Bjørnsen put Lillestrøm through in a 1–0 victory over Faaberg.