Hawzah News Agency (Sydney, Australia) – The man, believed to be in his 30s, entered the mosque on Burwood Road at Belmore about 12.45pm on Friday, police have been told.
He allegedly yelled obscenities at the congregation before he was escorted from the building and police were alerted.
The man has been described as Caucasian in appearance, with an athletic build, short blonde hair and sporting tattoos on his left inner forearm and side of his neck.
Police have urged anyone with information to come forward.
"To enter a place of worship and threaten the congregation is very concerning and disturbing to us," Detective Inspector Paul Albury said in a statement on Saturday.