The museum says the gun is an addition to its collection of "new, influential, innovative or experimental" contemporary design.
The "Liberator" gun was developed by University of Texas law student Cody Wilson, and made from plastic components created on a 3-D printer.
Wilson fired the gun in May, and posted blueprints online, sparking a debate about potential uses of the machines, which pump out layers of plastics, metal and other materials to create 3-D objects with moving parts.