The jet is one of hundreds of Boeing aircraft grounded around the world while investigators work to find the cause of an Ethiopian Airlines crash that killed 157 people earlier this month.
The 737 Max 8, Boeing's newest plane, has been involved in two crashes in less than six months. The first, in October, killed all 189 passengers and crew aboard a Lion Air flight when the plane plunged into the Java Sea in Indonesia shortly after takeoff.
The FAA said it is investigating today's incident.
"The crew of Southwest Airlines Flight 8701, a Boeing 737 MAX aircraft, declared an emergency after the aircraft experienced a reported engine problem while departing from Orlando International Airport in Florida about 2:50 p.m. today," the FAA said. "The aircraft returned and landed safely in Orlando. . . . The FAA is investigating."
The FAA announced the grounding of more than 70 Max aircraft in operation in the United States three days after the Ethiopian Airlines crash, and after reports of similarities between that March 10 crash and the Lion Air Flight 610 plane that crashed in Indonesia on October 29.
The grounding of the Max aircraft has affected thousands of travellers recently. Airlines have warned travellers about possible disruptions and the likely need to rebook for passengers who were originally scheduled to be on a Max jet.
Airlines say they have been rerouting aircraft through their networks to cover many of the 737 Max schedules to avoid flight cancellations. American and Southwest combined have 58 Max 8s in their fleets. United Airlines has 14 of the Max 9 planes, which were also grounded.
Some 737 Max 8s were still flying in US airspace this week as airlines continued to reposition their aircraft. No passengers were on board.