In the recent years, research on intelligent educational systems has attracted significant interest in exploring data from educational settings to understand learners' behavior and mental states. Hence, the means to deduce the mental state of a learner has been obtained from a variety of physiological indices. The current study aims to understand how a learner answers a question with confidence. By measuring the brain activity and eye movement by using a set of multiple-choice questions, this study analyzes the relationships between the confidence of answering the question, brain activation and eye movement at the time of answering. When there was a high confidence of answering, oxyHb tended to increase near the prefrontal cortex frontal pole and sight line movement to reread question text tended to decrease. The results show that this technique may be able to capture the mental state of the learner by measuring a combination of the change of oxyHb and sight line movement.