Scuffles broke out at anti-lockdown rallies in Athens and Thessaloniki.
Protesters launched fireworks at police, who deployed tear gas and arrested several.
Hundreds had gathered, denouncing government measures put in place to curb the spread of COVID-19.
Athens metropolitan area has been placed under a full lockdown to ease pressure on hospitals amid increased admissions.
Non-essential shops and schools are closed until the end of February.
Greece has registered 172,128 COVID-19 cases and 6,126 related deaths (according Johns Hopkins University).
