Metacognitive evaluations refer to the processes by which people assess their own cognitive operations with respect to their current goal. Little is known about whether this process is susceptible to social influence. Here we investigate whether nonverbal social signals spontaneously influence metacognitive evaluations. Participants performed a two-alternative forced-choice task, which was followed by a face randomly gazing towards or away from the response chosen by the participant. Participants then provided a metacognitive evaluation of their response by rating their confidence in their answer. In Experiment 1, the participants were told that the gaze direction was irrelevant to the task purpose and were advised to ignore it. The results revealed an effect of implicit social information on confidence ratings even though the gaze direction was random and therefore unreliable for task purposes. In addition, nonsocial cues (car) did not elicit this effect. In Experiment 2, the participants were led to believe that cue direction (face or car) reflected a previous participant's response to the same question-that is, the social information provided by the cue was made explicit, yet still objectively unreliable for the task. The results showed a similar social influence on confidence ratings, observed with both cues (car and face) but with an increased magnitude relative to Experiment 1. We additionally showed in Experiment 2 that social information impaired metacognitive accuracy. Together our results strongly suggest an involuntary susceptibility of metacognitive evaluations to nonverbal social information, even when it is implicit (Experiment 1) and unreliable (Experiments 1 and 2).