Unga is BYU's all-time leading rusher with 3,455 yards and is the first BYU player to rush for more than 1,000 yards in three consecutive seasons.
"I am staying in school and looking forward to playing my final season of college football," Unga said in a statement released by the school. "I want to finish my college education, and I hope to play well and do my best as a senior to help our team."
Unga led the Mountain West in rushing with 1,087 yards this season despite missing the season opener with a hamstring problem and missing significant time in three other games with injury.
Unga has a chance to become just the ninth player in the NCAA Football Bowl Subdivision to rush for more than 1,000 yards in four consecutive seasons. That feat was accomplished in each of the last two seasons by players from nonautomatic qualifying conferences -- Louisiana-Lafayette's Tyrell Fenroy in 2008 and Southern Mississippi's Damion Fletcher this season.
Graham Watson covers college football for ESPN.com.