Maxwell Air Force Base in Alabama resumed operations on Friday afternoon after the investigation of a suspicious package revealed it contained food, an air base spokesman said.
The package, the size of a box of blank checks, had earlier tested positive for explosive materials during a routine inspection at the base post office, causing officials to shut down part of the base for several hours.
Officials closed an entrance to the base in Montgomery around 10 a.m. local time (1600 GMT) and evacuated some buildings or asked people within the cordoned area to stay in place as a safety precaution.
All base operations returned to normal around 1:30 p.m. local time, a spokesman said.
Maxwell is home to more than 12,500 active-duty, reserve, civilian and contractor personnel, according to the base website.
(Reporting by Colleen Jenkins and Karen Brooks; Editing by Cynthia Johnston and Dan Grebler)