The arrests happened as the activists tried to organise a demonstration against Egyptian President Hosni Mubarak in al-Tahrir (Liberation) Square in central Cairo.
George Ishaq, a Kefaya (Enough) spokesman and general coordinator, and Amin Iskander, a senior leader in Kefaya, were among the 15 members detained.
They were held for several hours before being let go.
Speaking to Aljazeera by telephone after his release, Ishaq said the actions of the security forces showed that the government would not tolerate more demonstrations ahead of presidential elections set for September.
Aljazeera's correspondent said journalists covering the demonstration were harassed by police and minor skirmishes occurred between them and security forces.
Mubarak said he would seek a fifth six-year term in the country's first presidential elections with more than one candidate on 7 September.
Kefaya and other opposition groups have called for a boycott of the presidential election and charge that the 77-year-old Mubarak will seek a fifth mandate before attempting to hand over power to his son Gamal.