Perceptual grouping is a process involved in chunking of visual information and image segmentation, constituting an important aspect of visual processing. In this study, we analysed EEG gamma-band activities in a similarity grouping task to study brain mechanisms of perceptual grouping. It was found that an increase in induced gamma-band activity depended on the displayed position of the target quadrant. Induced gamma-band activity was mainly observed in the frontal and occipital areas for latencies of 370–630 ms. In addition, it was found that the duration of induced gamma-band activity reflected the level of difficulty of the task. Thus, we have shown that the neural activities involved in a similarity grouping task are characterized by the appearance of induced gamma-band activity and its continuation.