Officials from both the Nuclear Regulatory Commission and Florida Power & Light said that the $130,000 fine was paid in January.
A federal investigation found that six guards at FPL's Turkey Point nuclear plant slept or served as lookouts for other sleeping guards between 2004 and 2006.
The guards were contracted by Wackenhut Corp.
Officials say none of the guards remain on the job.
The commission's chairman said the plant was nevertheless safe and secure during a tour in May. The nuclear plant is about 30 miles south of Miami.