Police say the device was thrown while police were attending a road traffic accident in Castlemara Drive, Carrickfergus at around 1.05 am.
Inspector Mick Wood said although no injuries or damage was caused, the attack had to be condemned.
“A police officer should never come under attack while simply doing their job,” he said.
“The police service belongs to the whole community and police officers are there to serve and protect the whole community.”
He appealed for anyone with information to contact police on the 101 number or on Crimestoppers on 0800 555 111.