Ahmet Altan, a writer and former editor-in-chief of the Taraf newspaper, and his brother Mehmet were detained for questioning over their comments on a TV show a day before the putsch, according to local media reports and P24, an Istanbul-based association supporting independent journalism.
Taraf, one of dozens of media outlets closed since the coup attempt, was seen as close to the network of U.S.-based cleric Fethullah Gulen, blamed by Turkey for orchestrating the failed putsch. The cleric denies any involvement.
Turkish prosecutors and police could not immediately be reached for comment.
Turkey has detained more than 100 journalists since the events of July 15, in which rogue soldiers commandeered tanks and fighter jets, bombing parliament and other key buildings in an attempt to seize power.
Tens of thousands of police, soldiers, judges and civil servants have been purged on suspicion of links to Gulen, drawing criticism from rights groups and some Western allies, who fear a wider attempt to silence dissent.
Some of the journalists detained are known for their leftist activism and not for sharing the religious world view of the Gulenist movement.
Turkish officials reject such concerns, saying the extent of the crackdown is justified by the gravity of the threat to the Turkish state on July 15, when more than 240 people were killed, many of them civilians. Those found not to have links to the coup plot will be released, the officials say.