A Football Association statement explained why Mascherano, sent off by referee Steve Bennett for dissent amounting to a second bookable offence at Old Trafford on Sunday, is facing the fresh charge.
The statement reads: "The charge relates to his reaction towards referee Steve Bennett after being sent off against Manchester United on Sunday, March 23.
"He has until 6pm tomorrow to respond. The case will be heard by a regulatory commission on Friday, April 4.
"Mascherano is currently serving a one-match suspension for the sending-off."