If you stand mute, the court will enter a not guilty plea, so just enter a NG plea yourself. Standing mute is only in the Criminal rules when a defendant wishes not to enter a plea, this way he can be tried without any Due Process violations or is unable to actually enter a plea due to incompetency.
This is from the FL Rules of Criminal Procedure:
RULE 3.170. PLEAS
(c) Standing Mute or Pleading Evasively. If a defendant stands mute, or pleads evasively, a plea of not guilty shall be entered.

