Another 55 men were detained in the town of Fayyoum, south of the Egyptian capital.
Gaza siege outcry
Egypt is under increasing domestic pressure over the situation at the Gaza border.
The arrests are the latest in a crackdown on the Brotherhood, Egypt's most powerful opposition group.
Those detained include Saad Zaghloul, the secretary general of the Cairo doctors' syndicate, security sources said.
The Brotherhood said the detained men had organised protests on Tuesday and Wednesday.
"No to the siege of Gaza," protesters chanted in Cairo. "Break the bonds, remove the barriers," others shouted.
The Muslim Brotherhood, a non-violent group that the Egyptian government considers an illegal organisation, says Egypt should unilaterally open the border with Gaza.
Members of the Brotherhood hold a fifth of the seats in parliament and operate openly within limits, although security forces often detain members without formal charges.
More than 400 members of the group are currently in detention.