Reappraisal is an emotion regulation strategy which involves changing the interpretation of emotional stimuli. It decreases measures of negative affect together with markers of emotional processing, including late positive potential (LPP). Affective responses can also be attenuated by various cognitive tasks. As reappraisal tasks require cognitive effort to elaborate emotional stimuli, it is possible that the observed reduction of the LPP amplitude during reinterpretation is, at least partly, caused by an unspecific cognitive activity. The aim of the study was to examine, whether mental activity other than cognitive change carried out directly on affective stimuli can be a factor that significantly modifies the intensity of the emotional responses. Three groups took part in an experiment with standardized emotional pictures: a reappraisal group (trained in reinterpretation), a retro group (trained in cognitive elaboration of emotional stimuli other than cognitive change), and a control group (passive viewing). The early LPP potential showed a main effect of group with the highest amplitude in the control group and the lowest amplitude in the reappraisal group. The retro group revealed no significant differences comparing with the other two groups. The late LPP was indistinguishable in the reappraisal and retro groups, which showed an equal decrease in its amplitude compared to the control group in the case of negative stimuli. Conversely, behavioral ratings collected in a separate group of subjects showed a decrease in negative feelings in the reappraisal group only. We conclude that the LPP component during reappraisal is under additive influence from the cognitive change itself and from unspecific cognitive activity; however, both of them differ in regard to their temporal characteristics.