The alert was raised after a suspicious package was found at the consulate in the Italian business hub of Milan, but no explosives were found, according to leading daily Corriere della Sera.
The ANSA news agency said earlier that the consulate had received a letter referring to an explosive device.
"The US Consulate has re-opened and is operating normally. We are grateful for the prompt and professional response by Italian authorities," said Jen Psaki, spokeswoman for the US State Department.
The United States has closed two dozen US embassies in the Middle East and north Africa after its spies intercepted militant communications, reportedly including an attack order from Al-Qaeda leader Ayman al-Zawahiri.
On Tuesday it evacuated dozens of diplomatic staff from Yemen after its spies intercepted militant communications, reportedly including an attack order from Zawahiri.