A man attacked the agent with a knife, the source said.
None of the knife stabs penetrated the agent's body armor and the agent only suffered minor injuries, the complaint said.
Mr. Mumuni’s violent response to law enforcement was similar to the arrest on Saturday of Munther Omar Saleh of Queens for involvement in the same alleged plot.
Relatives and lawyers for Saleh and Mumuni have said they deny the charges. One of his co-conspirators had a knife in the waistband of his trousers.
The other man, who was also arrested, has not yet been publicly identified. He quickly cut off contact with the FBI source, saying he was ordered by ISIS to do so.
Saleh has been held without bail since Saturday and was arrested after he and an accomplice tried to attack an officer who was tailing his Jeep, according to authorities.
Court records show the two had discussed an attack against law enforcement in early June.
The documents said he was found to have searched online on how to build a pressure cooker bomb, like the one used in the Boston Marathon bombings.
A Queens-based student has also been detained for "plotting a bomb".
A further investigation into Saleh’s activities uncovered possible plans to detonate an explosive device in New York City on behalf of the terror group, court documents said.
The FBI reached this conclusion after monitoring Saleh’s communications and his use of social media, and conducting physical surveillance.
In September 2014 he allegedly tweeted "i fear AQ (al-Qaida) could be getting too moderate" and this year expressed support for the gunmen who attacked the Charlie Hebdo magazine in France.
Investigators say they began paying attention to him in late March, after he was twice seen walking around on the George Washington Bridge. Fortunately, this threat didn’t materialize due to the indefatigable efforts of the FBI’s Joint Terrorism Task Force.
In May, Saleh researched various tourist sites and landmarks in New York and their security surveillance.
He also viewed images on the Internet of New York City attractions, which officials said were likely targets for a terror attack.
FBI agents believed those items would be key to the construction of an explosive device.
And he searched online for firearms, knives, ammunition, masks and a bulletproof vest as well as beards and wigs, which could be fashioned into disguises. He also searched for information about remote-controlled helicopters and drones.
"Years ago you could be satisfied that the war was far away from you, and unfortunately that’s not the case anymore", ex- Boston Police Commissioner Edward F. Davis said of the arrest yesterday of Fereed Mumuni, 21, accused of trying to stab an FBI agent at his home yesterday morning before telling investigators he had pledged allegiance to the Islamic State and intended to attack police here if he couldn’t join the jihad in Iraq or Syria.
Mumuni is charged with attempting to kill a federal agent.