Words that are more predictable given a previous context show facilitated processing over low predictable ones. Such facilitation has been traditionally viewed as associated with reduced amplitudes in the N400 component. However, this effect is observed during the presentation of the target word, and it does not provide direct information about the prediction processes engaged before. To overcome this, we investigated neural correlates of anticipation prior to target words using an auditory paradigm. The semantic context of the sentences varied in the degree of contextual constraint, with sentences of high, low or no constraint. The final word presented could be either congruent –the best completion– or incongruent. We inserted a noticeable 1000 ms delay before the final word of a sentence. The ERP analysis of the delay period unveiled a slow potential, with an amplitude that was more negative as contextual constraint increased. We also observed a canonical N400 modulation to semantic fit and cloze probability, and we report, for the first time to our knowledge, a delay in the onset of the N400 effect for low levels of contextual constraint. This study provides novel electrophysiological data that contributes to the better comprehension of the processes involved in speech processing with evidence in favour of anticipatory models of language processing.