Worshippers found a severed pig's head when they arrived at the Canberra Islamic Centre in Monash on Monday morning.
Police are reviewing CCTV footage from the centre after the head was found on the driveway about 5.10am, a spokeswoman said.
President Azra Khan said the incident was nothing new for the organisation.
The centre came under attack several times last year, with vandals causing hundreds of thousands of dollars of damage in April.
Three people tried to break into the centre in October but fled when they noticed the CCTV cameras, installed after the April attack.
"It's not upsetting any more; it's just a nuisance," Mrs Khan said.
"It's nothing overly concerning or new … we're not overreacting to this."
The police spokeswoman urged anyone who may have seen or heard suspicious activity between midnight and 5am on Monday in Monash to contact Crime Stoppers on 1800 333 000.
Information can be provided anonymously.