Per ESPN's Adam Schefter, Roberts will sign a one-year deal with the Ravens.
The Ravens were in the market for another wide receiver after releasing Michael Crabtree and losing John Brown in free agency.
After going undrafted out of West Alabama in 2014, Roberts joined the Raiders as practice squad player in his first season. He made the 53-man roster in 2015 and has been one of their most productive wideouts over the past four years.
Roberts set career highs with 45 receptions and 494 yards in 2018.