Brett McMurphy reported the Gators' decision to hire Mullen.
The 45-year-old Mullen was hired after the second title by the Bulldogs and has a 69-46 record in nine seasons at the school.
Mullen also reportedly was under consideration for the Tennessee job.
AP's source said the Gators are Mullen are working toward a deal.
Mississippi State head coach Dan Mullen, left, and Mississippi head coach Matt Luke wish each other good luck prior to the start of an NCAA college football game in Starkville, Miss., Thursday, Nov. 23, 2017.
Mississippi State has won its last two bowl games, most recently defeating Miami (Ohio) in the St. Petersburg Bowl a year ago.
There were some rumors that Florida could turn it's attention to UCF's Scott Frost, who is responsible for the Knights' incredible turnaround, but Nebraska seems like a more likely option for him.
Mullen replaces Jim McElwain, who was sacked in midseason.
In 9 years at Mississippi State, the Bulldogs have reached new heights: 8 straight bowl appearances, reaching #1 in the polls in 2014, playing in the Orange Bowl, recruiting and developing National Football League talent like Dak Prescott, Fletcher Cox, and Chris Jones.
All along, Florida officials have wondered whether Mullen would be the best fit because of his time at the school, his SEC experience and his success developing quarterbacks.