This paper presents a steady-state visual evoked potential (SSVEP) based online brain-computer interface (BCI) chatting system. In this application, it helps disable subjects to chat by means of their brain signal activities. Stimuli illuminated at different frequencies are displayed on liquid crystal display (LCD) screen. The BCI system implements a chatting interface programmed in Java, and it provides a convenient and high efficient communication platform for paralyzed patients. A novel idle state detection is introduced in this proposed system, and a high transfer rate of 63.54 bits/min and 92% idle state detection accuracy are achieved.