Some of them were detained after attending a meeting of Iran's largest student group -- Daftar Tahkim Vahdat, or the Office To Foster Unity -- while others had held a sit-in at Tehran University to mark the anniversary of student unrest in 1999.
Tehran authorities had banned gatherings commemorating the 1999 unrest, when hardliners attacked a university dormitory, killing one person and sparking days of rioting and protests.
Rights activists say pro-reform students, labor activists, and intellectuals have been targeted in recent months in what they describe as a fresh crackdown on dissent.
Law enforcement agencies have also intensified their crackdown in recent years against what they describe as immoral and un-Islamic behavior.
In the latest move, Iranian police today announced that they detained 20 people in a raid on what they called a "decadent gathering" in the city of Karaj, near Tehran.
The arrests came a week after 230 people were arrested in a raid on a gathering in Karaj that authorities described as a Satan-worshipping underground rock concert.
(Reuters, AFP, ISNA, IRNA)