In Western tonal music, the rules of harmony determine the order and music-structural importance of events in a musical piece: for instance, the tonic chord, built on the first note of the diatonic scale, is usually placed at the end of chord sequences. A brain response termed the early right anterior negativity (ERAN) is elicited when a harmonically incongruous chord is inserted within or at the end of a musical sequence. The present study was conducted to test whether the ERAN reflects the processing of harmony rather than the building of a tonal context and whether the ERAN is also elicited by violations of the tuning of the sounds upon which harmony is based. To this aim, ten subjects listened to musical sequences containing either expected chords only, a harmonically incongruous chord in one of three positions within the cadence, or a harmonically congruous but mistuned chord in one of the three positions. Simultaneously, the electroencephalograph (EEG) was recorded. Incongruous chords violating the rules of harmony elicited a bilateral early anterior negativity, the amplitude of which depended on the degree of the harmony violation. On the contrary, mistuned chords, violating the rule of relations between all the sounds in the sequences, elicited a bilateral fronto-central negativity (the mismatch negativity, or MMN). The MMN was not modulated by the position of the violation within the musical sequence and had a longer peak latency than the anterior negativity elicited by the harmony rule violations. In conclusion, violations of the harmony and tuning rules of Western tonal music were found to generate specific and distinct electric responses in the human brain.