Uncertainty is unavoidable, and maladaptive responses to uncertainty may underlie the etiology and maintenance of psychopathology. A general tendency to associate uncertainty with aversive consequences, a type of covariation bias, can amplify aversive emotional experiences. To address questions about uncertainty during emotion regulation, we examined the Late Positive Potential (LPP) - an electrocortical marker of attention to and appraisal of motivationally relevant emotional stimuli - during a task designed to measure the effect of covariation bias and its emotional response consequences. Event-related potentials (ERPs) were recorded while participants ( N = 52) were presented with a pre-stimulus cue that either conveyed information about the valence of an upcoming emotional image, or left them in ambiguity. We replicated findings that demonstrate expectancy biases in a priori and online expectancies of emotion-eliciting images, as well as in a posteriori estimates for concurrence of uncertainty cues and aversive images. Moreover, we demonstrate a novel finding that uncertainty cues amplify the LPP in response to subsequent aversive emotional stimuli. These findings advance research by conjoining existing emotion regulation research on the LPP with study of the effects of uncertainty on emotional appraisal and highlight the importance of accounting for stimulus uncertainty in emotion regulation research.