Brain-Computer Interface (BCI) performance suffer from various variability sources, including intra-subject factors such as mental fatigue. While frequently measured using subjective reports, mental fatigue can also be assessed via blink parameters extracted from electro-oculography signals. To our knowledge, no study has yet evaluated blink parameters during motor imagery (MI) BCI use to assess the potential development of mental fatigue. In this study, the blinks of 23 MI-BCI participants were analyzed concurrently with subjective reports and BCI performance. Our results showed that blink parameters were correlated with neither MI-BCI performance nor subjective reports. However, they revealed a positive correlation between time-on-task and both blinks number and mean duration. Similarly, subjective fatigue was correlated with time-ontask. This suggests that blinks parameters may be useful for BCI user monitoring, although their relationship with BCI performance and fatigue needs further studies. Altogether, this study paves the way towards a better understanding of mental fatigue during BCI use, and in finding solutions to mitigate it.