Watching motivationally relevant pictures modulates two types of event-related brain potentials (ERPs), the early posterior negativity (EPN) and the P3. Several studies show that the EPN and P3 to emotional stimuli are enhanced as compared to neutral stimuli. The goal of the present study was to investigate whether experimentally conditioned abstract stimuli (Gabor patches) that predict the occurrence of a subsequent emotional event are able to elicit an enhanced EPN and P3. This would confirm that these ERP components indeed reflect the motivational relevance of a stimulus, rather than other stimulus properties such as complexity. In a conditioning paradigm, abstract patches (conditioned stimuli; CS) were contingently paired with emotional or neutral pictures (unconditioned stimuli; UCS). Both EPN and P3 to these CS were measured in 80 healthy participants. The results demonstrate an enhanced P3 to CS predicting emotional stimuli as compared to CS predicting neutral stimuli. The EPN was not modulated by the CS. These results show that the P3 is a suitable index of acquired motivational relevance and is not, at least not completely, dependent on task-irrelevant stimulus properties such as complexity and contrast. The EPN seems less suitable as an index of recently acquired motivational relevance because, although the CS acquired emotional significance, this did not result in the typical EPN modulation.