The deal is pending a physical. The team didn't disclose financial terms of the agreement.
Roberts didn't remain unemployed for long after the Raiders released him Thursday. He spent five seasons with the franchise but was waived after the team continued its off-season overhaul of its receiving corps.
The Ravens parted ways with veteran wideout Michael Crabtree and saw receiver John Brown join the Buffalo Bills in free agency, leaving the team with a need at the position. Willie Snead and Chris Moore are the current leaders of the Ravens' wideout group.
Oakland originally signed Roberts as an undrafted free agent in 2014 out of West Alabama. He spent his entire rookie season on the team's practice squad.
Roberts made the Raiders' final roster in 2015 and played in all 16 regular-season games the next two seasons. In five NFL seasons, he has appeared in 62 games (25 starts) and tallied 158 catches for 1,826 yards and 13 touchdowns.
It's the second consecutive season that the Ravens added a former Raiders receiver in the off-season. Baltimore signed Crabtree from Oakland last year.