Gustafsson, 26, who is a resident of Stockholm, originally revealed the bout to Sweden-based website Kimura.se. UFC officially announced the showdown Saturday.
Gustafsson (15-1) is ranked sixth among light heavyweights by ESPN.com. He put himself in the 205-pound title conversation on Dec. 8 with a unanimous decision over former UFC champion Mauricio Rua.
His lone setback occurred in April 2010 against fellow contender Phil Davis -- Gustafsson was submitted in the first round.
Mousasi will make his UFC debut against Gustafsson. He was among a group of fighters added to UFC's roster earlier this week after Strikeforce held its final event on Jan. 12 in Oklahoma City.
During the final Strikeforce event, Mousasi improved to 33-3-2 with a first-round submission win over Mike Kyle.
ESPN.com's Josh Gross contributed to this report.