There are no reports of any casualties.
A spokesman said: "Police are currently in attendance at an ongoing incident after an object was thrown at police lines from the Brompton Park area of north Belfast."
It is understood a loyalist protest against a decision to ban Protestant Orangemen from marching past a nationalist area was taking place at the time of the attack.
Army bomb experts have been called to the scene and the Crumlin Road has been closed between Tennent Street and Twaddell Avenue.
It is understood the device detonated on the ground after it struck an armoured PSNI vehicle.
Terry Spence, chairman of the Police Federation which represents rank and file officers, said police were in a difficult position.
"We have been here so many times before where the police are the meat in the sandwich. Quite clearly this demonstrates how police officers have to be alert and very cautious looking over their shoulder while carrying out public order duties. They can come under gun or bomb attack at any stage. It is a worrying development but sadly it is not new."
SDLP MLA for north Belfast Alban Maginness has condemned the attack. He said: "After three nights of violence in north Belfast the PSNI have now been subjected to a pipe bomb attack in Brompton Park in Ardoyne. This is completely unacceptable and I am very glad to hear that no one was injured in this needless and cowardly attack.
"This is a time now for cool heads and I would urge restraint on the community lest the violence that we have witnessed over the past few nights spread and grow."