Coach Bobby Bowden would not give details of the violation, but said McPherson would remain in school and on scholarship through the end of the semester.
"That's about all I can say," Bowden said. "This is kind of new to me, too."
Bowden called his decision to dismiss McPherson "clear cut."
At the end of Monday's news conference, sports information director Rob Wilson said the investigation did not involve gambling or point shaving.
No one has been charged in the check forgery, and police would have no further comment until criminal charges are filed, the Tallahassee Police Department said in a statement.
The 19-year-old McPherson will not play basketball, either. Last season, he played in three games before deciding to concentrate on football. He is the only Florida prep athlete to be named "Mr. Basketball" and "Mr. Football."
McPherson replaced Chris Rix following a 34-24 loss Oct. 26 to Notre Dame, going 3-1 in four starts. The two were scheduled to compete for Saturday's start after McPherson struggled in a 17-7 loss Saturday at North Carolina State.
After meeting with McPherson, Bowden informed Rix that he would be the starting quarterback in Saturday's game against No. 23 Florida (8-4, 7-1 Atlantic Coast Conference). Fabian Walker will be the backup.
Rix has completed 53.6 percent of his passes for 1,490 yards and 11 touchdowns. He has been intercepted seven times.
"I'm more eager and anxious than I've ever been to get back on the field," Rix said, adding he was saddened by McPherson's dismissal.
"It's a shock," Rix said. "It's out of our hands. I feel for Adrian and his family. Hopefully, we can help him out anyway possible."
McPherson was 80-of-155 for 1,017 yards with 12 touchdowns and one interception in nine games this season. He was replaced by Rix for the final drive in a 17-7 loss Saturday to North Carolina State.
McPherson led Florida State to victories over Wake Forest, Georgia Tech and North Carolina. Though his numbers through those three games were not spectacular -- 51-of-98 for 654 yards -- McPherson threw one interception while throwing eight touchdowns.
Against NC State, the Seminoles did not score an offensive touchdown and McPherson struggled, completing 8 of 20 passes for 80 yards. He missed several open receivers and was sacked several times, taking Florida State out of field-goal range.