The minicamp is mandatory for all players under contract. Bell has not signed his franchise tender and can't be fined for his absence.
Bell, who is coming off groin surgery, has until the July 15 deadline to work out a deal for franchised players. If not, the 25-year-old Bell will play the 2017 season on the $12 million franchise tender.
The Steelers rode Bell to the playoffs last season. He rushed for 1,268 yards (4.9-yard average) and seven touchdowns in 12 games, and caught 75 passes for another 616 yards and two scores during the regular season, becoming the first player in NFL history to average 100 rushing yards and 50 receiving yards per game.
Bell set franchise single-game rushing records in the first two playoff games. He racked up 167 yards in a victory over the Miami Dolphins in the AFC wild-card round and bettered that with 170 in the win over Kansas City Chiefs in the divisional round.