Understanding Quality of Experience (QoE) in various multimedia contents is still challenging. In this paper, we investigate the way QoE affects brain oscillations captured by electroencephalography (EEG). In particular, sixteen subjects watched 2D and 3D videos of various quality levels while their EEG signals were recorded, and were asked to provide their self-assessed perceived quality ratings for each video. EEG signals were decomposed into six frequency bands, namely theta, alpha, beta low, beta middle, beta high and gamma bands. The results revealed frontal asymmetry patterns in the alpha band, which correspond to right frontal activation when perceived quality is low. This finding implies that perceived high quality may be related to positive emotional processes.