Turnbull briefed on terror arrest

Prime Minister Malcolm Turnbull says terrorism is a "serious, ever-present threat" in Australia.

Mr Turnbull was briefed on Wednesday by the Australian Federal Police on the arrest and charging of a 17-year-old Sydney boy with two terrorism-related offences.

"We have to be vigilant constantly - this is a serious, ever-present threat," Mr Turnbull told reporters in Perth.

NSW Premier Mike Baird said the teenager was facing serious charges.

"Being detained on terrorism charges is very serious, and again a reminder we have to be as vigilant as we can.

"From the advice I have, it's not related to any previous incidents so this is a new incident," Mr Baird told reporters in Sydney on Wednesday.

"Clearly our police are doing everything they possibly can to protect us and keep us safe, and obviously I congratulate them for taking the steps that they have."