Perceptual expectations can change how a visual stimulus is perceived. Recent studies have shown mixed results in terms of whether expectations modulate sensory representations. Here, we used a statistical learning paradigm to study the temporal characteristics of perceptual expectations. We presented participants with pairs of object images organized in a predictive manner and then recorded their brain activity with magnetoencephalography while they viewed expected and unexpected image pairs on the subsequent day. We observed stronger alpha-band (7-14 Hz) activity in response to unexpected compared with expected object images. Specifically, the alpha-band modulation occurred as early as the onset of the stimuli and was most pronounced in left occipito-temporal cortex. Given that the differential response to expected versus unexpected stimuli occurred in sensory regions early in time, our results suggest that expectations modulate perceptual decision-making by changing the sensory response elicited by the stimuli.