Halk TV said its employees were unable to enter the building in Istanbul and that a new manager had been appointed to run the channel.
The station is widely seen as close to the opposition Republican People's Party (CHP) and frequently carries criticism of Mr Erdoğan's ruling AK party.
The raid follows other setbacks for the opposition. In May, a Turkish court removed the CHP leadership from running the party, a legal move the opposition said further cemented Mr Erdoğan's grip on power. Istanbul Mayor Ekrem Imamoğlu, widely regarded as the president's biggest political rival, has been in prison for more than a year over corruption accusations he denies.