The Court for Urgent Matters has upheld the designation of the Muslim Brotherhood as a terrorist group.
The interim government declared the Brotherhood a terrorist group in December but the decision had not been approved of by a court until now.
The Brotherhood has been blamed for militant attacks since the ouster of Mohamed Morsi – a longtime member of the group – in July 2013.
The attacks have mainly targeted the security forces, with the exception of a bomb in South Sinai in February that killed four civilians, including three South Korean tourists.
The Brotherhood has repeatedly condemned the attacks and denied responsibility for them.