A method of producing a mouldable fiber reinforced plastic sheet in which at least one of the reinforcing fiber layers is a woven or non-woven fabric of carbon fibers, that can be used as a heating element. The carbon fibers are bonded together by plastics which contain thermoplastics. Upon application of electric current the sheet warms quickly and evenly and a suitable voltage is 0,1 - 380 V. The current strength and the voltage can vary.