A statement by the prosecution said the court rejected the appeal by the five defendants.
The men were convicted in November of "spying for and seeking with Iran and its agents to carry out hostile acts against the kingdom", a judicial sources said at the time.
They were found guilty of working with Iran's elite Revolutionary Guard to carry out attacks in Bahrain against public facilities and banks.
Two of them had received training in Iran on "the manufacture and use of explosives and firearms in preparation for carrying out these hostile attacks", according to the charges.
The Shiite-majority kingdom, connected to Saudi Arabia by a causeway, lies across the Gulf from Shiite Iran and is home to the US Fifth Fleet.
Despite the crackdown on the 2011 uprising, protesters still frequently clash with police in Shiite villages outside the capital Manama.