The Bulgarian signed for Villa from Lech Poznan in 2013 and failed to score in eight starts and only 20 appearances for the West Midlands club.
Tonev spent last season on loan with Scottish giants Celtic but will now head to Italy with the best wishes of Villa.
TRANSFER NEWS: Good luck to Aleksandar Tonev who has today joined @Frosinone1928 on a permanent deal. #AVFCpic.twitter.com/4U4dGVrCUl
— Aston Villa FC (@AVFCOfficial) August 27, 2015