The deal is worth $15 million and includes $9 million in guarantees and another $1.8 million in incentives, a source told ESPN.
Bethel, 25, was selected to the Pro Bowl the past two seasons as a special teamer. In 59 games he has 63 tackles on special teams and has blocked three field goal attempts.
Despite playing 210 snaps on defense this season, Bethel is the 25th-ranked cornerback out of 113, according to Pro Football Focus.
On Sunday, playing the final quarter and a half after Jerraud Powers suffered a calf strain, Bethel allowed two catches on three targets for 21 yards against the 49ers. He's allowed 48.1 percent of targets thrown at him to be caught this season.
Bethel has allowed 136 receiving yards this season, including 38 after the catch, along with one touchdown. He also has an interception, which he returned for a touchdown in Week 3 against San Francisco.
Bethel was a 2012 sixth-round pick by the Cardinals out of Presbyterian College.
Information from ESPN.com's Josh Weinfuss and ESPN Insider Adam Schefter was used in this report.