In this poster we introduce a novel approach, called the "Mind-Window", for real-time visualization of brain activity. The Mind-Window enables one or multiple users to visualize the brain activity of another person as if her skull was transparent. Our approach relies on the use of multiple tablet PCs that the observers can move around the head of the observed person wearing an EEG cap. A 3D virtual brain model is superimposed onto the head of the observed person using augmented reality by tracking a 3D marker placed on top of the head. The EEG cap records the electrical fields emitted by the brain, and they are processed in real-time to update the display of the virtual brain model. Several visualization techniques are proposed such as an interactive cutting plane which can be manipulated with touch-based inputs on the tablet. The Mind-Window could be used for various application purposes such as for Education as teaching tool to learn brain anatomy/activity and EEG features, e.g., electrodes localization, electrical patterns, etc.