The head of Egypt's state NGO federation will be detained for 15 days while prosecutors investigate allegations against him, judicial sources told Ahram Online on Tuesday.
Hatem Khater, who is also a senior member of the Muslim Brotherhood, is accused of inciting violence and joining an outlawed group, the sources said.
The Brotherhood, which worked underground for decades before it won successive elections following the downfall of autocratic president Hosni Mubarak, was banned by a court order in September.
In its 23 September ruling, the court also banned "any institution branching out from or belonging to the Brotherhood."
Khater endorsed a consensual decision by the NGO federation to ban the Brotherhood's NGO, which had only been registered in March.
He is a co-founder of two prestigious charities: Egypt's Food Bank and the Egyptian Cure Bank.
Authorities have rounded up most of the Brotherhood's senior leaders, including its highest authority, Supreme Guide Mohamed Badie, over allegations of inciting violence. Former president Mohamed Morsi has been detained since his ouster on 3 July and is due in court on 4 November on similar charges.