Kuwait's interior ministry said on Friday the Egyptians belonged to a "terrorist" cell linked to the Brotherhood. They had fled to Kuwait after being sentenced by Egyptian authorities to jail terms of up to 15 years, it said.
Kuwait has not specified the circumstances of their sentencing, and there has been no official comment on the case from Egyptian judicial authorities either.
The men were returned under the terms of bilateral agreements, KUNA quoted a senior foreign ministry official as saying late on Sunday. The interior ministry said investigations were ongoing to discover other cell members.
Egypt banned the group in 2013 after late Muslim Brotherhood President Mohamed Morsi, the first democratically elected head of state in Egypt's modern history, was toppled by the military following widespread unrest.
Since then, Egyptian authorities have arrested tens of thousands of political opponents, many of them Islamists, according to human rights organisations.
The Brotherhood says it publicly renounced violence decades ago and pursues an Islamist political vision using peaceful means.