Resumo. BACKGROUND: The fronto-central slow-wave known as the contingent negative variation (CNV) is an electroencephalographic measure related to the ability of the motor system to extract spatial-temporal regularities to produce a motor response. AIM: This study aimed to investigate the levels of electrocortical activity prior to predictable and unpredictable stimuli in a motor control task, and the association between CNV and reaction time (RT). METHOD: Seventeen participants performed a task that consisted of removing the right index finger from the space bar as fast as possible after stimulus onset. All participants practiced under both a predictable (PC) and an unpredictable (UC) context.  RESULTS: Results indicated that RT under the unpredictable context was slower than under the predictable context. However, CNV levels under predictable and unpredictable contexts did not differ. CONCLUSION: The certainty of stimulus appearance in the UC may have produced effects similar to those under the PC, resulting in similar CNV levels. However, the use of this mechanism under the UC was suboptimal to motor performance.