Australia on Monday raised its terrorism threat level from "possible" to "probable", with the country's top intelligence official citing a homegrown rise in "extreme ideologies".

Intelligence chief Mike Burgess said there was no indication of an "imminent attack", but there was an increased threat of violence in the next 12 months.

"Australia's security environment is degrading, is more volatile and more unpredictable," Burgess told reporters.

"You've heard me say many times that espionage and foreign interference are our principal security concerns... intelligence suggests that is no longer accurate.

"Politically motivated violence now joins espionage and foreign interference as our principal security concerns."

Burgess, the head of the Australian Security Intelligence Organisation, said "more Australians are being radicalised" and the country was battling "spikes in political polarisation".

Earlier this year, a 16-year-old suspect stabbed an Assyrian Christian bishop during a Sydney church service in what police said was a religiously motivated "terrorist" act.