Mobley accepted a football scholarship to Washington State University in Pullman, where he was a four-year starter at strong safety under head coachMike Price. He also was used as a kickoff returner in some situations. As a freshman in 1991, he collected 33 tackles, one interception and one forced fumble. As a sophomore in 1992, he had 75 tackles, 3 tackles for loss, 4 passes defensed, one interception, one forced fumble and one fumble recovery. The Cougars won the Apple Cup in the snow in Pullman and the Copper Bowl in Tucson, Arizona. In 1993, he registered 63 tackles, 4 tackles for loss, 2 interceptions, 3 passes defensed, 2 sacks and 2 forced fumbles. As a senior in 1994, he recorded 55 tackles, 1.5 tackles for loss, 5 passes defensed, one fumble recovery and one forced fumble.
Professional career
Edmonton Eskimos (first stint)
Unselected in the 1995 NFL Draft, Mobley signed with the Edmonton Eskimos of the Canadian Football League. He had 58 tackles, 3 fumble recoveries and one sack. In 1996, he posted 72 tackles, 5 sacks, one interception and one fumble recovery.
On February 12, 1997, he was signed as an undrafted free agent by the Dallas Cowboys, reuniting with former Cougars defensive coordinator Mike Zimmer, who was the team's defensive backs coach. He was one of thirteen rookies to make the team. He was declared inactive in four of the first 5 games. He finished seventh on the team with 11 special teams tackles. In 1998, he was sixth on the team with 10 special teams tackles. He spent three seasons with the Cowboys as a backup safety and special teams player. He wasn't re-signed at the end of the 1999 season.
Edmonton Eskimos (second stint)
On May 23, 2000, Mobley was signed by the Edmonton Eskimos and was switched to linebacker. He led the team in tackles in 2004 and 2005. In 2006, he was second on the team with 59 tackles. He was released after the season and announced his retirement on May 24, 2007. In all, Mobley played 158 games over nine seasons with the Eskimos, was a part of two Grey Cup championship teams, registered 602 tackles, 21 sacks, 24 passes defensed, 15 interceptions and 78 special teams tackles. In 1995, he set a team record with 129 yards in fumble recoveries. He is considered to be one of the greatest defensive players in franchise history.