Using a classical conditioning technique, this study investigated whether nonconscious associative learning could be indexed by event-related brain activity . There were three phases. In a preconditioning baseline phase, pleasant and unpleasant facial schematics were presented in awareness . A conditioning phase followed, in which stimuli were presented outside awareness , with an unpleasant face linked to an aversive shock and a pleasant face not linked to a shock. The third, postconditioning phase, involved stimulus presentations in awareness . Evidence for (...) acquisition of a conditional response was sought by comparing suprathreshold pre- and postconditioning phases, as well as in the subthreshold conditioning phase itself. For the pre-postconditioning phase analyses, significant ERP component differences differentiating CS+ and CS− were observed for N1, P2, and especially P3. For the conditioning phase, significant differences were observed in the 100–400 ms. post-stimulus region reflecting a CS+ processing negativity. Brain activity does indeed index the acquisition of a conditional response to subthreshold stimuli. Associative learning can occur outside awareness. (shrink)