The person spoke to The Associated Press Wednesday on condition of anonymity because the move has not been publically announced.
Mitchell played in 61 games with nine starts during four seasons with the Oakland Raiders. He had 41 tackles last season and one sack.
The team moved Charles Godfrey to free safety last season.
On his Twitter page, Mitchell thanked the Raiders, saying: "Oakland will always be in my heart" but added, "I look forward to the opportunity to be a Carolina Panther."