Police said Nguyen Lan Thang, 47, who lives in Dong Da District, is under investigation for "making, storing and/or circulating documents and/or cultural products with contents against the Socialist Republic of Vietnam."
On his Facebook account with more than 150,000 followers, he had recently posted content designed to undermine the state.
At the time of arrest Tuesday afternoon, the account was still active.
According to the Penal Code, those facing similar charges can face five to 12 years in jail. In cases of "especially serious" violations, the jail term could be up to 20 years.