Airport spokesman Greg Chin says a note found in one of the plane's bathrooms Thursday night said an explosive device might be on board. American Airlines Flight 1640 had departed Miami International Airport around 9:30 p.m.
Airline spokesman Billy Sanez says the plane was searched after the 168 passengers and six crew members disembarked safely. He declined to say if anything suspicious was found.
The passengers stayed overnight in Miami and were scheduled to leave for Boston on Friday morning.
The threat remains under investigation.