Someone made a phone call this morning reporting noises that could have been shots, the Montgomery County Police said.
The center announced a shelter in place order soon after the call was made. However, officers responded and found no confirmed shots and no reported injuries, police said.
Officers finished searching the Walter Reed tower this afternoon, police said.
Patient care at the facility is suspended for the rest of the day, the Montgomery County Police tweeted.
The Navy originally confirmed the lockdown in a statement, saying: "All base personnel are sheltering in place as a result of unconfirmed reports of an active shooter."
The Navy's statement added: "DOD Security Force, NIH Police Force and County EMS and Medics have responded and searching the area."
The National Naval Medical Center and Walter Reed Army Medical Center joined in 2011, forming the Walter Reed National Military Medical Center, one of the largest military medical centers in the U.S.