The restroom is an area of Terminal 2 not open to the general public, FBI spokeswoman Laura Eimiller said in a statement.
The FBI and other agencies "will investigate the incident to determine the individual or group responsible," Eimiller said.
No injuries were reported, and Terminal 2 resumed operations after a brief evacuation.
Terminal 2 is the airport's "secondary international terminal," airport spokesman Nancy Castle said.
™ & © 2013 Cable News Network, Inc., a Time Warner Company. All rights reserved.