It happened at approximately 5:30 a.m. at Omar Mosque in Paterson.
A spokesperson for the mosque says the suspect lunged forward with a knife and stabbed the imam.
The suspect reportedly attempted to flee, but congregants were able to hold him down until police arrived and arrested him.
"This is a senseless crime, but one that we strongly believe is an isolated incident," said Abdul Hamdan, the masque's spokesperson. "Because of the swift action of the Omar Mosque congregants, the attacker was swiftly and immediately apprehended."
Officials say the imam is in stable condition.
The violent outburst occurred during Ramadan, the holiest month on the Muslim calendar.