ESPN's Jeremy Fowler reported Bell didn't show up with the rest of the team and is not subject to fines since he has yet to sign his one-year franchise tender worth $12.1 million.
Via Twitter, Steelers wide receiver Antonio Brown pleaded with Bell to show up to camp:
The move wasn't surprising, since Bell previously skipped Steelers minicamp last month while holding out for a long-term contract.
The deadline for players designated with the franchise tag to sign long-term deals was July 17. Bell rejected the Steelers' offers.
NFL Network's Tom Pelissero reported Pittsburgh's long-term offer included $30 million in the first two years, $42 million over three years and an average annual value of $12-plus million. NFL Network's Ian Rapoport reported it was a five-year offer.
Bell has established himself as one of the NFL's best running backs over the past four seasons. The 25-year-old has 4,045 rushing yards, 2,005 receiving yards and 86 total touchdowns in 47 games since being drafted 48th overall in 2013.