The three young men were allegedly carrying birdshot, banners with slogans supporting the Brotherhood and opposing the military government and broadcast cameras, Ahram Online reported. Investigators say they were planning to incite trouble at two universities in Cairo.
They were arrested in Nasr City, a Cairo neighborhood that is home to a university and was the site of a major Brotherhood sit-in during the summer.
Mohamed El-Beltagy was taken into custody in August. Another son was detained briefly, and his 17-year-old daughter, Asmaa, was killed in a crackdown on a Brotherhood camp in Cairo on Aug. 14.
The government declared the Brotherhood a terrorist organization last week.