The unconscious arithmetic calculations (single-digit multiplication) were studied. The masked priming paradigm was applied. To test the possibility of unconscious arithmetic operations the event related potentials method was used. The arithmetic N400 effect served as calculations correctness criterion. The influence of training on the N400 component formation during stimuli unconscious perception was revealed. The results of this study confirm the possibility of unconsciously executing simple operations for multiplication. The N400 arithmetic effect can be used to study reflex calculations at an unconscious level.