US personnel were told to take shelter at RAF Lakenheath, a major base hosting American forces in the UK, following "suspected unauthorised drone activity".
No one was affected, nor was any aircraft.
"This evening, USAF Security Forces personnel responded to suspected unauthorised drone activity over RAF Lakenheath. No personnel, aircraft or infrastructure were affected," a US Air Force spokesperson said.
"We continue to work closely with our host nation counterparts to ensure the safety and security of our US service members, US and host nation civilians, contractors, and all of our families. Protecting our shared community is a joint responsibility, and we encourage everyone to support this effort by reporting any unusual or suspicious activity to local authorities."
Sky News has seen a copy of an alert that instructed personnel at RAF Lakenheath to "shelter in place".
Nick Timothy, a local MP, wrote on social media that he had been in touch with the authorities and "there is no threat to the public and the incident is now resolved".
The alert message that was sent to personnel was headed in capital letters with the words "REAL WORLD" written in red.
It instructed people on the base to "shelter-in-place".
It said: "Seek the nearest shelter-in-place room."
An MOD spokesperson said: "We are coordinating with all relevant parties regarding reports of unauthorised drone activity at RAF Lakenheath this evening. USAF Security Forces personnel responded to the reports and the situation is now resolved. We are working closely with them to establish the facts. We will provide updates in due course."
The incident came after the US military on Monday evacuated more than a dozen warplanes from a second, sprawling airbase in Suffolk, RAF Mildenhall, amid reports of a security threat linked to Iran.
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At least two of the aircraft were moved to RAF Lakenheath.
Last month, the US moved its bomber planes from a third British base, RAF Fairfield, following threats again linked to Iran, sending them back to the United States.
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