Naval Support Activity Bethesda includes a number of facilities, including the Walter Reed National Military Medical Center.
The base added on Twitter that it received an anonymous phone call at around 8:45 a.m. ET about a bomb in one of the buildings.
Earlier, the base said that it was investigating an active shooter threat. Later, it said there is no signs of a shooter on the premises.
“At this time, there is no indication of an active shooter on the installation,” Naval Support Activity Bethesda wrote. “A bomb threat is still under investigation. A lockdown remains in place.”
An official “all clear” directive will be sent out by the base on its social media and other official channels when it is appropriate, it said.
Other than Walter Reed, Naval Support Activity Bethesda houses the Armed Forces Radiobiology Research Institute, Naval Medical Leader and Professional Development Command, and Soldier Recovery Brigade, among others.
“Go indoors into the nearest building and shelter in place. All commands initiate building emergency plans to shelter in place,” Walter Reed also wrote on Twitter.