Australia will indefinitely detain people convicted of terrorism-related charges if it feels they pose an ongoing danger to society upon their release, Prime Minister Malcolm Turnbull has said.

Mr Turnbull cited the spate of recent attacks such as the Bastille Day massacre in Nice, which killed at least 84 people, and said the measures are designed to deter terrorism and keep Australians safe.

"It will provide a very real incentive for people in prison for terrorist offences not to engage in continued extremist activity," the prime minister told reporters.

Attorney General George Brandis said indefinite detention would be decided by a court-supervised process, which includes medical and psychological assessments, and details of a prisoner's behaviour in custody.

There will also be a periodic review, an annual report to parliament, and a statutory review of the efficacy and need for the scheme after the first several years, Mr Brandis said.

"I make no apology for the government taking the view that if a person, having served a sentence of imprisonment for a serious crime, shows every indication of a willingness to repeat that crime, to reoffend as soon as they are released, they should remain behind bars," Mr Brandis told the Australian Broadcasting Corporation.

Australia has been on heightened alert for attacks by home-grown radicals since 2014, having suffered several "lone wolf" assaults, including a cafe siege in Sydney in which two hostages and the gunman were killed.

Last month, Australia's immigration ministry said around 100 people have left Australia to fight alongside groups such as the so-called Islamic State in Syria.