The discovery was made by a highway maintenance worker along the westbound lanes near Braddock Mountain.
Authorities can only say that it's the body of an adult. No identification was found with it.
The body was in a box, barely visible off the shoulder of the highway in a wooded roadside embankment.
It's not known how long it's been there.
Maryland's medical examiner is conducting an autopsy while investigators look for clues to the identity of the victim.