The Raiders announced the move on their website Saturday.
Oakland placed the tag on Seymour in February, making him unable to negotiate with any other teams. Raiders coach Tom Cable said the sides had been working on a long-term deal but Seymour decided to sign the one-year tender.
The Raiders are done with their offseason program so Seymour will join them when training camp starts in Napa on July 28.
The Raiders acquired Seymour just before the start of last season by sending a 2011 first-round pick to New England. Seymour finished with four sacks in 15 games.