Keller, 6-foot-4 and 235 pounds, went undrafted out of Nebraska earlier this year. He worked out for the Tampa Bay Buccaneers and the Raiders within the first two weeks after the NFL draft.
"Obviously, there are some people out there who don't think I can play," Keller told the Lincoln Journal Star after he wasn't draft. "(Draft) weekend was disappointing. But I guess it's just some more adversity for Sammy."
Keller, 23, signed a three-year contract with the Los Angeles Avengers of the Arena Football League last month but jumped at the chance to earn a backup spot at quarterback with the Raiders.
Russell is the unquestioned starter at this point. Beyond that, Andrew Walter and Marques Tuiasosopo are the leading candidates for the Nos. 2 and 3 spots, based on their NFL experience.
It is unclear whether Raiders coach Lane Kiffin intends to carry three or four quarterbacks on the opening-day, 53-man roster. Kiffin carried four at times last season.
Keller will compete for a roster spot with Walter, Tuiasosopo and Jeff Otis. The Raiders waived rookie quarterback Erik Meyer to make room for Keller.
In other news, the man who allegedly robbed and beat Raiders wide receiver Javon Walker on June 16 in Las Vegas told a judge
"She was forced by the police, because of the other matter, to go forward with these accusations," Arfat Fadel said as he appeared by videoconference before Las Vegas justice of the peace Eugene Martin.
Las Vegas Police spokesman Ramon Denby declined to comment on Fadel's accusation because investigations were continuing in both cases. He said Fadel had not cooperated with investigators in their attempts to identify a second man suspected of beating Walker.
Fadel faces multiple felonies, including kidnapping, robbery, battery and conspiracy in the incident that left Walker bloodied and unconscious on a Las Vegas street. Fadel is scheduled to make his initial appearance on those charges today in Las Vegas Justice Court.