Event-related potentials (ERPs) to tones that are self-initiated are reduced in their magnitude in comparison with ERPs to tones that are externally generated. This phenomenon has been taken as evidence for an efference copy of the motor command acting to suppress the sensory response. However, self-initiation provides a strong temporal cue for the stimulus which might also contribute to the ERP suppression for self-initiated tones. The current experiment sought to investigate the suppression of monaural tones by temporal cueing and also whether the addition of self-initiation enhanced this suppression. Lastly, the experiment sought to investigate the lateralisation of the ERP suppression via presenting these monaural tones to each ear respectively. We examined source waveforms extracted from the lateralised auditory cortices and measured the modulation of the N1 and P2 components by cueing and self-initiation. Self-initiation significantly reduced the amplitude of the N1 component. Temporal cueing without self-initiation significantly reduced the P2 component. There were no significant differences in the amplitude of either the N1 or the P2 between self-initiation and temporal cuing. There was a significant lateralisation effect on the N1-it being significantly larger contralateral to the ear of stimulation. There was no interaction between lateralisation and side of the temporal cue or side of self-initiation suggesting that the effects of self-initiation and temporal cuing are equal bilaterally. We conclude that a significant proportion of ERP suppression by self-initiation is a result of inherent temporal cueing.