The Post Office at Marine Corps Base Quantico was closed Monday morning while authorities investigated a suspicious powder Monday morning.
The object, however, tested negative for any dangerous substance.
Quantico officials said on their Facebook page that a suspicious package containing the powder was discovered at the base's post office Monday morning.
Four people, including two Marine postal specialists, a civilian postal clerk and a customer, were inside when the powder was found. No one was injured or sickened.