A brain–computer interface (BCI) is a direct communication channel between brain and external devices without any use of peripheral nerves and muscles. The key issues in BCIs are brain signal recordings and interpretations. Scalp EEG-based BCI is a non-invasive technology, and probably the most acceptable systems for the subjects to use. The comprehensive EEG signal analysis in EEG-base BCI are described in this paper, and the designs of the on-line EEG-based BCI systems are also presented.