The six, five Turks and a foreign national, were detained in the southeastern city of Gaziantep in a raid on a house, the Anatolia news agency reported.
It did not say when the raid took place, but said police had been watching the group for some time.
One of the men, whom Anatolia identified as Fahad Abdurrahman El Cakmak, had travelled to Pakistan and Afghanistan, the report said.
Police seized several passports and identification cards and were inspecting a computer used by the group, Anatolia said.
Police in Gaziantep, about 700km southeast of Ankara, would not comment on the report.
More than 70 suspected al-Qaeda militants, including a Syrian, are on trial in Istanbul for alleged involvement in a series of bombings that killed 58 people in the city in 2003.
The Syrian, Loa'i Mohammad Haj Bakr al-Saqa, was allegedly the head of an informal court that sentenced kidnapped British engineer Kenneth Bigley to death in Iraq in 2004.