According to the August edition of Jump SQ this year, which will be released on July 4, 2016, Ao no Exorcist (Blue Exorcist) will be getting a sequel anime scheduled to air in 2017. It will adapt the Impure King arc from the manga.
The official website has recently displayed a countdown timer that is still running. The timer is scheduled to end on July 4.
The series previously received a first season anime adaptation in 2011 and a movie anime adaptation in 2012.