Prominent activist Ahmed Douma was arrested at his home in Cairo and taken to a police station on Tuesday morning, he said via Twitter.
He did not specify the reason for his arrest.
In April 2013, Douma was detained for calling president Mohamed Morsi a killer and a criminal. Douma later said he was fined LE20,000 in the case.
The young activist accompanied April 6 Youth Movement co-founder Ahmed Maher when he handed himself in to police earlier this week over breaking the protest law.
Egypt's new protest law requires protest organisers to notify authorities three days in advance of a protest's aims and demands, imposing jail terms and fines on individuals who break the law.
Douma, an activist since the Mubarak era, was also arrested in 2012 – when Egypt was ruled by a military council – following clashes with soldiers outside the cabinet building near Cairo's Tahrir Square.