If true, it would be the first public message from him in about a year and would dispel rumours that he is dead, BBC reported.
The voice on the audio calls on Iraqis to defend the city of Mosul against the Iraqi army, which is attempting to re-take it from the militants.
Baghdadi’s whereabouts remain unknown. Some officials have said he may be inside Mosul alongside IS fighters.
It has not been independently verified that the voice in the audio belongs to Baghdadi. There have been repeated rumours of his death through the years, including last year when the Iraqi military said it had hit his convoy.
Mosul, the last IS urban stronghold in Iraq, is where Baghdadi declared a caliphate two years ago.