Police blocked access to the site of the event in central Moscow and arrested group co-founder Vadim Korovin.
RosAgit had planned to hand out free camping tents for possible use in long-term street protests following the March 4 presidential vote, which Vladimir Putin is set to win in a landslide.
The distribution was seen as a call on Putin opponents to occupy public spaces in protest at election results, in a repeat of the 2004 Orange Revolution in Ukraine.
Activists from Nashi, the combative pro-Kremlin youth group, were present at the event and threatened to confiscate the tents for their annual summer youth camp at Lake Seliger.
RosAgit's Korovin, who was released several hours after his arrest, said police had told him he was the main suspect in an alleged armed robbery earlier in Moscow of a vehicle carrying camping tents.
-- Claire Bigg