Leto, 43, posted a picture on Instagram of him recording a track in the studio, with the hashtag #MarsIsComing, reported Digital Spy.
The band haven't released any new music since 2013's Love, Lust, Faith and Dreams, which reached number 5 in the UK album charts.
But the Academy Award winner is teaming up with his brother Shannon and bandmate Tomo Milicevic once again to make a new record.
Leto can next be seen as the Joker in "Suicide Squad" which will officially hit cinemas on August 5, 2016.