Mordecai, who spent the past two seasons as the Sooners' backup quarterback, announced his decision via Twitter.
Mordecai, a redshirt sophomore this season, will have three years of eligibility remaining, because of the NCAA's blanket waiver that allowed all players to compete this season without it counting against them. The 6-foot-2, 211-pound Mordecai is a Texas native, playing his high school ball at Midway High in Waco.
An ESPN 300 recruit in the 2018 class, Mordecai appeared in 12 games in his Oklahoma career, completing 50-of-70 pass attempts for 639 yards, four touchdowns and one interception. He backed up Jalen Hurts in 2019 and Spencer Rattler in 2020.
Mordecai will join what is likely to be an open competition for the starting quarterback job after two-year starter Shane Buechele recently declared for the NFL draft. The Mustangs also recently signed Preston Stone, a 2021 ESPN 300 quarterback recruit from Dallas, during the early signing period.