Columns of protesters defied a government warning to march in front of soldiers and military vehicles. They waved red-and-white opposition flags and shouted "go away!" and "we won't forget, we won't forgive!".
Lukashenko has been in power since 1994 and, buoyed by a show of support from traditional ally Russia, has rejected calls for new elections from Sviatlana Tsikhanouskaya, his main opponent who fled into exile two days after the vote.
Demonstrations have carried on throughout the four weeks since the election, gaining in size on the weekends and drawing tens of thousands of people each Sunday.
The interior ministry said in a statement that 91 protesters had been detained on Saturday, and said it would beef up security and take "take all necessary measures to suppress such actions and prevent violations of public order" on Sunday.