The Raiders say Reece signed the contract on Monday in time to participate in organized team activities.
Reece had not been part of offseason workouts with the team under new coach Dennis Allen's staff before signing the one-year deal.
Reece has played in 30 career games with 16 starts since joining the Raiders as an undrafted free agent in 2008. He has 54 career receptions for 654 yards and five touchdowns, and 47 carries for 234 yards and one score.
Reece will be eligible to be a restricted free agent next offseason and an unrestricted free agent following the 2013 season.