The incident happened after 9:00 a.m.
Authorities say an on duty employee at United Airlines, believed to be a cargo worker, got into a dispute with someone else, possibly another employee.
Officials said he took an airline vehicle and drove around secure areas at Newark International Airport for about 10 minutes.
He was eventually stopped by Port Authority Police on the ramp side of building 344.
He was not armed, but authorities questioned him for several hours. No charges were expected, officials said.
United issues a one sentence statement regarding the incident: "A United employee was detained by authorities this morning following a security procedural irregularity at Newark Liberty International Airport."
There was no disruption to air travel.