Sheppard was signed by Oakland on Friday and was expected to join the team at practice ahead of its matchup Sunday against the New Orleans Saints, according to the Bay Area News Group.
A first-round pick by the Eagles in 2002, Sheppard has bounced around the league in recent seasons. The two-time Pro Bowler spent 2010 with the Minnesota Vikings after a one-year tour with the New York Jets.
Sheppard, 30, will fortify a secondary that is without injured cornerbacks Chris Johnson, a projected starter, and rookie DeMarcus Van Dyke. The Raiders were already in a transition period following the free-agent defection of Nnamdi Asomugha to the Eagles.