Bucky Turco of Brooklyn took the photograph Sunday and posted it online. His link was sent to TSA officials.
The unidentified agent has been reassigned to desk duty pending the investigation's outcome.
She might have been on a break. TSA spokeswoman Ann Davis said agents have very demanding jobs. But Davis said they should use break rooms instead of resting in public areas.
Another TSA worker was placed on administrative leave for allegedly leaving his post at Newark Liberty International Airport.
A man there breached security to kiss his girlfriend; the scare closed a terminal for six hours.