In a statement, Muaaz Saad Katatni, the son of the Freedom and Justice Party (FJP) Chairman, confirmed his father was arrested.
"Nearly 12 men, in civilian clothes, came to our house to arrest my father. They took him away to an unknown location.
"My heartfelt congratulations to him. We take pride in being arrested for our homeland. We will do as God wishes. May he enable us to persevere."
Muaaz denounced the manner in which military coup enforcers dealt with the head of Egypt's largest political party, saying:
"Those who claim to defend freedoms and democracy, invited my father for dialogue in the afternoon (in reference to the army invitation for Katatni to sit for dialogue earlier on Wednesday) then arrested him in the evening.
"Welcome to the new era of freedoms!"