User authentication plays an important role in security systems. In general, there are three types of authentications: password based, token based, and biometrics based. Each of them has its own merits and drawbacks. Recently, the research communities successfully explore the possibility that electroencephalography (EEG) being as a new type of biometrics in person recognition, and hence the prospect of using EEG in user authentication is promising. An EEG-based user authentication system has the combined advantages of both password based and biometric based authentication systems, yet without their drawbacks. In this paper we propose to use EEG to authenticate users in multilevel security systems where users are asked to provide EEG signal for authentication by performing motor imagery tasks. These tasks can be single or combined, depending on the level of security required. The analysis and processing of EEG signals of motor imagery will be presented through our experimental results.