Improving user performances is one of the major issues for Motor Imagery (MI)-based BCI control. MI-BCIs exploit the modulation of sensorimotor rhythms (SMR) over the motor and sensorimotor cortices to discriminate several mental states and enable user interaction. Such modulations are known as Event-Related Desynchronization (ERD) and Synchronization (ERS), coming from the mu (7-13 Hz) and beta (15-30 Hz) frequency bands. This kind of BCI opens up promising fields, particularly to control assistive technologies, for sport training or even for post-stroke motor rehabilitation. However, MI-BCIs remain barely used outside laboratories, notably due to their lack of robustness and usability (15 to 30% of users seem unable to gain control of an MI-BCI). One way to increase user performance would be to better understand the relationships between user traits and ERD/ERS modulations underlying BCI performance. Therefore, in this study we analyzed how cerebral motor patterns underlying MI tasks (i.e., ERDs) are modulated depending (i) on nature of the task (i.e., right-hand MI and left-hand MI), (ii) the session during which the task was performed (i.e., calibration or user training) and (iii) on the characteristics of the user (e.g., age, gender, manual activity, personality traits) on a large MI-BCI data set (N=70 participants). Our results confirmed a stronger ERD contralateraly, while we still observed a bilateral ERD overall. We also observed stronger ERD during calibration (with sham feedback) than during online training (with real-time feedback and instructions to explore promising MI strategies). Finally, and more importantly, our study revealed for the first time, associations between ERD and both age, level of study, impression management and anxiety. This may suggest that such factors should be taken into account when designing MI-BCI based on ERD or when selecting an ERD-based BCI for a given user.