An improvised explosive device was hurled from the nationalist Brompton Park area of Ardoyne and exploded after striking an armoured police vehicle just after 5pm.
There were no reports of any injuries.
Witness Sam Coulter, who was yards from the explosion at a loyalist protest, said it was fortunate no one was hurt.
We were standing having a peaceful protest when all of a sudden there was a bang and the next thing we heard the 'tinkle, tinkle, tinkle' of nails dropping on the ground.
I think it was directed at the protest - police were at the other side of the road behind a Land Rover. Luckily nobody was hurt - just a bit of a bang to the ears.The place is in lockdown now with police doing sweeps of the area to gather evidence.
This won't put us off our protest - we are still here.