In our study, we addressed the question of whether and how the learning process of a novel category and uncertainty in our knowledge about it is reflected in ERP responses and alpha-band suppression of the brain. To test these ideas, we built our experimental procedure on the oddball paradigm that is frequently used to investigate the nature of category representations in the human brain. Contrary to the majority of similar studies, we used continuous stimuli and recorded ERPs from the beginning of learning omitting any training before the actual data collection. Obtained results suggest that participants mapped correctly the proper statistical distribution of the input both in their implicit judgments and explicit decisions about the learnt boundary between the two acquired categories. Uncertainty followed this mapping as higher uncertainty reports were localized along the implicit category boundary. Neural signatures of the emerging internal representations allow us to track the formation of categories. Increased amplitude of P300 ERPs reflects the level of suddenness of an observed stimulus, and alpha-suppression corresponds to the learner’s subjective confidence in their knowledge about certain exemplars of a category during learning. These results support the ideas that ERP and alpha-suppression are reliable signals of not only the already acquired structure of concepts, but they also allow for tracking the ongoing acquisition of categories.