A leading member of Rouvikonas (Greek for Rubicon) was detained Monday after he warned on Facebook that the anti-establishment group planned to target popular tourist spots with their protest stunts.
Reports identified the man as Giorgos Kalaitzidis.
Meanwhile, two members of the group were charged by an Athens prosecutor Monday in connection with the vandalism on Sunday of the Hellenic Federation of Enterprises (SEV) headquarters near central Syntagma Square.
Both will stand trial on charges of damaging private property.
Greece’s new center-right government has pledged to crack down on anti-establishment groups who, for their part, have vowed to resist.