"Rashad al-Bayoumi and seven others are still being detained" after their arrest by Egyptian police on Friday, Mahmud Ezzat, a senior Brotherhood official, said on Saturday.
Al-Bayoumi is on the Brotherhood's 13-member Guidance Bureau, an advisory council for the Brotherhood leadership. He was arrested at his home in a Cairo suburb.
Essam al-Aryan, a top leader of the group, said the arrests reflected the Egyptian government's state of confusion.
But Major-General Fouad Allam told Aljazeera that the arrest of Brotherhood activists was justified.
On Friday, Egyptian security forces arrested seven student activists from the Brotherhood, an official for the group said.
Abdul Munem Mahmoud, the Brotherhood official, said seven members of the group, all university organisers, were arrested during a raid on their Cairo apartment.
"Security men broke into the apartment and arrested the young men and took them to an unknown destination," Mahmoud said.
"They were only arranging a protest against the offensive cartoons of our great prophet."
A police officer confirmed the arrests. "The men attached to the Brotherhood were having a meeting in their place, which is banned by the government," said the officer.
The Brotherhood in December said authorities detained more than 1250 of its supporters during parliamentary elections - mostly in retaliation for the group's success at the polls.
The Brotherhood emerged from Egypt's parliamentary
elections with nearly 20% of the seats, establishing a powerful opposition bloc.