Moudasser Taleb, 22, from Sydney's southwest was nabbed as he tried to leave the country on Thursday morning, allegedly to travel to the Syrian war zone to fight with Islamic State.
Police claim the Australian-born man intended to purchase a plane ticket to Lebanon or Turkey.
"We believe he was acting alone and was radicalised himself," Deputy Commissioner Dave Hudson told reporters in Sydney.
"It appears he was radicalised online."
Taleb, of Middle Eastern background, who was known to police for minor matters, was engaging with people overseas and had taken a taxi to the airport to purchase a ticket to travel overseas, Mr Hudson alleged.
Taleb - wearing tracksuit pants, joggers and a woollen beanie - was handcuffed and escorted out of Sydney Airport by two plain-clothes officers, a police photo shows.
"Actions taken this morning were to taken not only to protect the people of NSW but more broadly overseas," Australian Federal Police Assistant Commissioner Ian McCartney told reporters.
Taleb is expected to be charged and face a Sydney court later on Thursday.
