Various reports, including MLB.com, have indicated that the deal is worth $500,000. He is expected to report to the A's spring training as a non-roster invitee by the end of this week.
Ramirez played just five games with Tampa Bay last April and suddenly announced his retirement after a second violation of the league's Joint Drug Prevention and Treatment Program. The penalty would have included a 100-game suspension, but he instead chose to hang up his cleats.
In December, Ramirez applied for reinstatement. The Office of the Commissioner and the Players Association then decided that Ramirez must first serve a 50- game suspension.
Ramirez, a 12-time All-Star who will turn 40 years old on May 30, previously served a 50-game ban in 2009 as a member of the Dodgers for his first drug violation.
In 19 seasons with the Indians, Red Sox, Dodgers, White Sox and Rays, Ramirez has batted .312 with 555 home runs and 1,831 RBI. He won World Series titles with Boston in 2004 and 2007, capturing MVP honors in the 2004 sweep of St. Louis.