Affective judgments can often be influenced by emotional information people unconsciously perceive, but the neural mechanisms responsible for these effects and how they are modulated by individual differences in sensitivity to threat are unclear. Here we studied subliminal affective priming by recording brain potentials to surprise faces preceded by 30-msec happy or fearful prime faces. Participants showed valence-consistent changes in affective ratings of surprise faces, although they reported no knowledge of prime-face expressions, nor could they discriminate between prime-face expressions in a forced-choice test. In conjunction with the priming effect on affective evaluation, larger occipital P1 potentials at 145–175 msec were found with fearful than with happy primes, and source analyses implicated the bilateral extrastriate cortex in this effect. Later brain potentials at 300–400 msec were enhanced with happy versus fearful primes, which may reflect differential attentional orienting. Personality testing for sensitivity to threat, especially social threat, was also used to evaluate individual differences potentially relevant to subliminal affective priming. Indeed, participants with high trait anxiety demonstrated stronger affective priming and greater P1 differences than did those with low trait anxiety, and these effects were driven by fearful primes. Results thus suggest that unconsciously perceived affective information influences social judgments by altering very early perceptual analyses, and that this influence is accentuated to the extent that people are oversensitive to threat. In this way, perception may be subject to a variety of influences that govern social preferences in the absence of concomitant awareness of such influences.