Due to their relevance to one's optimal adaptation to their environment, emotional stimuli automatically capture heightened attention which facilitates their further processing and optimal behavioral outcomes. The influence of emotion on attention can be investigated with electroencephalography (EEG), specifically by employing the event-related potentials technique. P300 is positive potential with the maximal amplitude approximately 300 ms post-stimulus at midline electrodes which is usually elicited in an oddball task. It reflects categorization, comparison of new stimuli with previous ones and updating of the mental model in the working memory. The aim of our study was to investigate how the P300 is affected by the emotional content of the stimuli (negative or neutral), stimuli type (target or distractor) and categorization (based on emotional content or the presence of humans). During EEG recording 32 participants performed a visual three-stimuli oddball task with four conditions: identify negative stimuli, neutral stimuli, stimuli with people, and stimuli without people. In every condition we identified the P300 with the maximal parietal amplitude 500 ms post-stimulus and the late positive potential which persisted up to 1000 ms post-stimulus or longer. Both negative targets and negative distractors elicited larger P300 and late positive potential amplitudes than neutral ones between 370 and 1200 ms post-stimulus. Neither the type of categorization nor the type of stimuli affected the P300 and late positive potential amplitudes.