While listening to music, we immediately detect 'wrong' tones that do not match our expectations based on the prior context. This study aimed to determine whether such expectations can occur preattentively, as indexed by event-related potentials (ERPs), and whether these are modulated by attentional processes. To this end, we recorded ERPs in nonmusicians while they were presented with unfamiliar melodies, containing either a pitch deviating from the equal-tempered chromatic scale (out-of-tune) or a pitch deviating from the diatonic scale (out-of-key). ERPs were recorded in a passive experiment in which subjects were distracted from the sounds and in an active experiment in which they were judging how incongruous each melody was. In both the experiments, pitch incongruities elicited an early frontal negativity that was not modulated by attentional focus. This early negativity, closely corresponding to the mismatch negativity (MMN) of the ERPs, was mainly originated in the auditory cortex and occurred in response to both pitch violations but with larger amplitude for the more salient out-of-tune pitch than the less salient out-of-key pitch. Attentional processes leading to the conscious access of musical scale information were indexed by the late parietal positivity (resembling the P600 of the ERPs) elicited in response to both incongruous pitches in the active experiment only. Our results indicate that the relational properties of the musical scale are quickly and automatically extracted by the auditory cortex even before the intervention of focused attention.