The men were arrested in Marsa Matrouh, a vacation town on the Mediterranean coast 524 kilometers (325.5 miles) from Cairo. All were originally from the port city of Alexandria and were on a summer holiday, according to the group's Web site.
They were arrested for holding illegal meetings in three apartments, police officials said on condition of anonymity because they were not authorized to speak to the media.
The Muslim Brotherhood increased its seats in parliament sevenfold in last year's legislative elections, despite clashes between security forces and opposition voters that killed some 14 people.
The group, which holds 88 seats in parliament - still well short of a majority - is officially banned in Egypt, and membership is considered illegal, the AP reports.
The Muslim Brotherhood, founded in 1928 and banned since 1954, is Egypt's largest Islamic group and is believed to have tens of thousands of followers.