The punishment rules the Saint-Etienne player, 22, out of Norway's next four qualifying matches on the road to Russia 2018, the Norwegian FA said.
The incident came after a 1-0 defeat at Azerbaijan in early October.
According to the Norwegian FA, Selnaes told a FIFA disciplinary committee: "After the game I walked off the pitch and into the tunnel, where the linesmen were standing.
"As I passed him on my way to the changing room, I said to him, 'You referees whistled on everything, you are so fucking bad.' That was all."
Selnæs subsequently apologised but said he was disappointed by the punishment, which he described as "unreasonable," according to a Norwegian statement.
The Norwegian Federation has asked FIFA for clarifications before deciding whether to appeal.
Norway are fourth in Group C, behind leaders Germany, Azerbaijan and Northern Ireland and with their 2018 hopes in the balance.