Early right anterior negativity (ERAN) is an event-related potential elicited when a musical chord deviating from the tonality context is presented. Therefore, ERAN might reflect the syntactic processing of music and the sense of tonality. Recent studies have reported that music training enhances ERAN’s amplitude. However, findings on ERAN in people without musical training have been inconsistent. Moreover, the musical abilities affecting ERAN amplitude of non-musicians are unclear. This study investigated the relationship between ERAN and relative pitch ability in non-musicians using chords, including Neapolitan 6th as stimuli. The results confirmed that ERAN could be observed even in untrained people. Moreover, a high ERAN amplitude was associated with better relative pitch ability when it was difficult to detect deviancies in tonality. These findings suggest that the ERAN’s amplitude varies among non-musicians due to differences in their musical ability.