Cain was scheduled to become a free agent but avoided hitting the open market Thursday. Cain has been with the Jaguars for two seasons after being claimed off waivers from Washington in 2009. He played in all 32 games the past two years.
Cain had nine special-teams tackles in 2009 after earning a roster spot in the preseason. He had four special-teams tackles last season.
The Associated Press contributed to this report.