About 400 demonstrators flocked to Syntagma Square, outside the national parliament, after a rally was called on social media to protest coronavirus rules, according to the Proto Thema weekly.
A large banner comparing masks to muzzles and demanding that people "get our lives back" was unfurled in the crowd. Some people carried Greek flags and sang the national anthem.
Clashes erupted when a protester threw an orange at the police. Officers responded by firing tear gas. Several arrests were made and a woman needed medical care after she fainted.
Greece went into a nationwide lockdown in early November to limit the spread of the coronavirus. Those who refuse to wear a mask face a fine of 300 euros ($364).