The three activists, who are members of the feminist group Femen, appeared in front of the Palace of Justice wearing blouses, which they took off, Tunisia Live said.
Their chests were painted with slogans such as "Breasts Freed" and "Femen Sexetremist."
The three protesters chanted "Free Amina" and held banners with the Femen symbol, Tunisia Live said.
The protest was met with angry shouts from pedestrians walking by, including lawyers and court staff.
The Femen protesters were forcibly taken into court, and police arrested six journalists for taking photographs of the event, Tunisia Live reported.
Amina is charged with possession of pepper spray, officials said.