The ability to detect and process ambiguous information is an important cognitive skill facilitating our understanding of the environment. However, neural correlates of erroneous detection of ambiguity are still poorly understood. In this study we tested a prediction that a neural marker of erroneous perception, the so-called error-related negativity (ERN), may potentially reflect erroneous judgements of ambiguous input as unambiguous one. We used verbal ambiguities (jokes) and non-verbal graphical information (ambiguous figures). The results showed that ERN was elicited only when mistaking ambiguous figures for non-ambiguous ones, but not when mistaking verbal jokes for non-humoristic stories. We interpret these findings that the ERN might be indicative of both potential covert awareness of alternative meanings of the stimuli and the stimulus-response correspondence.