He was dismissed from the dugout during the 1-1 draw and needed a police escort from the pitch.
Warnock who, at the time, described the sending off as "unwarranted" has until May 12 to respond to the charge.
The Blades boss admitted an identical charge in April. He was charged by the FA after making a V-sign at Norwich City boss Nigel Worthington during the 2-1 defeat on March 18.