A nurse who said he was forced to work with the so-called Islamic State is thought to be returning to Australia.
Muslim convert Adam Brookman said he travelled to Syria last year to do humanitarian work, local media said.
Police have not named the returning man but confirmed an Australian involved in the conflict had turned himself in.
Mr Brookman would be the first person to return from Syria or Iraq since Australia made it a crime to assist militant groups in the Middle East.
He may face arrest when he arrives at Sydney airport.
The Melbourne nurse told Fairfax Media in May that he had travelling to Syria in 2014 to use his nursing skills to help people caught in Syria’s civil conflict, but was then was forced to help IS.
The Australian Federal Police (AFP) said the man’s return from Syria, via Turkey, was being managed “in co-operation with relevant local authorities”.
It said he had not been charged but was under investigation for his activities in Syria.
Under Australia’s Foreign Fighters legislation, it may be enough to simply be in Syria or Iraq to face charges.
The legislation has made it easier to ban terrorist organisations.
It also strengthened the offences of training with, recruiting for and funding terrorist organisations and made it easier to prosecute foreign fighters by making it illegal to travel to a declared area overseas.
In December, 2014, Australia proscribed travel to Syria’s Raqqa province, which is held by IS.
According to the government, at least 100 Australians are fighting with terror groups in the Middle East, and another 150 people in Australia are known to be supporting such groups.
Mr Brookman had said he believed Syria was being ignored by the international community.
“I thought I could help. I support the struggle of the Syrian people,” he had told Fairfax Media.
He said he was forced to join IS after being injured in an airstrike and taken to a hospital controlled by the militants.
Meanwhile, the body of an Australian man killed fighting with a Kurdish group in Syria will be returned to Australia on Friday.
According to the Australian Broadcasting Corporation, 23-year-old Reece Harding travelled to the Middle East in May to fight against IS militants and was killed after he stepped on a land mine.
A funeral for Mr Harding is expected to be held on Sunday.