The protests erupted in August, after the presidential election in which Lukashenko won about 80 percent of the vote. The opposition and its supporters claim that the election was rigged, and the president, who has been in office for 26 years, refuses to resign.
Police in riot gear stormed a rally on Friday, removing hundreds of protesters by truck.
The Vesna-96 group said 70 people had been detained.
Organizers of Sunday’s protest this week called on people to gather in dozens of different places in the city before forming a large group, making it difficult for police to control the crowd.
Demonstrations were rekindled by the death of a 31-year-old protester this month after he was beaten by law enforcement, according to protesters.
The interior ministry has denied responsibility for his death, saying it came after several civilians pushed.
Opposition leader Svetlana Tihanovskaia, who is in exile in Lithuania, welcomed the protest on Sunday. Lukashenko is declared a “persona non grata” in the Baltic countries, and the European Union refuses to recognize him as president of Belarus, as does Washington.