Police arrested 25 people for allegedly holding a public meeting, which requires police clearance in Zimbabwe.
The arrests took place when police on Saturday stormed the home of Costa Machingauta, a legislator with the opposition Citizens Coalition for Change (CCC).
The CCC said it was a private meeting.
State media, the only news outlets admitted at the start of the hearing, reported that the detainees filed a request for bail.
Tension was high outside the court, where anti-riot police armed with assault rifles, batons and teargas shoved other journalists away, an AFP reporter saw.
Defence attorney Kudzai Kadzere, who was not in court, said he had suffered a broken arm when he was assaulted by anti-riot police on Saturday as he approached a Harare police station where the activists were held.
Attacking a lawyer is "a new low for Zimbabwe," the Law Society of Zimbabwe said in a statement.
Critics have complained of a tightening clampdown on dissent and the media ahead of general elections due this year.
The CCC said at the weekend that Machingauta, his wife and 17-year-old daughter were beaten up before he was carried away.
Police refused to comment.
It was unclear whether Machingauta was among those who appeared in court on Monday.
CCC spokeswoman Fadzayi Mahere described the arrests as "calculated to persecute our members."
"We are continuing to see an escalation of political violence," she said outside the court. "This does not bode well for a free and fair election."