The 25-year-old Keiser had 4½ sacks in 12 games with the Chargers last season, third-most on the team. But he was mired at the bottom of the depth chart through the preseason.
To make room, the Cardinals released rookie wide receiver Walt Powell, a sixth-round draft pick.
The release of Powell leaves Arizona with five wide receivers.
Arizona also signed six players to the practice squad — linebacker Jonathan Brown, wide receiver Brittan Golden, tight end Andre Hardy, cornerback Jimmy Legree, tackle Kevin Palmer and guard-center Anthony Steen.