How are the learning process of a novel category and uncertainty about the category reflected in the alpha-band suppression of the brain? We built an experimental procedure on the oddball paradigm frequently used to investigate the nature of category representations in humans, but contrary to similar studies, we used a continuous stimulus dimension and recorded EEG signals from the beginning of learning. Behaviorally, we found that participants mapped correctly the statistical distribution of the input in their implicit judgments with higher uncertainty reports along the implicit category boundary. Confirming earlier results, we found significant differences in alpha ERD elicited by frequent and infrequent stimuli [t(11)=2.66, p<.02].