Mohammed Zubair, who co-founded Alt News and regularly tweets on rising marginalisation of the Muslim minority in the country, was arrested under two sections of a law related to maintaining religious harmony, said the DIGIPUB association.
Alt News's other co-founder, Pratik Sinha, said on Twitter no notice was given to Zubair before his arrest.
"He is currently detained inside a police bus in Burari for more than an hour," Sinha said, referring to a Delhi neighbourhood where Zubair was to be produced before a magistrate at his residence to authorise the journalist's remand.
A Delhi Police spokesperson did not immediately respond to a request for comment. Calls to their office phone went unanswered.
Reuters partner ANI reported, citing Delhi Police sources, that Zubair was arrested based on a complaint from a Twitter account that said he insulted Hindus in a 2018 post commenting on the renaming of a hotel after the Hindu monkey god Hanuman.
Journalists demanded his immediate release.
"Journalist Zubair who routinely busted fake news, exposed the hate machinery in India has just been arrested," said Rana Ayyub, another Muslim journalist who often invites the wrath of Hindu hardliners. "The country is punishing those who reported, documented the decline."
Ten human rights organisations said on World Press Freedom Day last month that Indian authorities were increasingly picking on journalists and online critics for their criticism of government policies and practices, including by prosecuting them under counter-terrorism and sedition laws.
Government officials deny the charges.