In the educational Serious Games (SGs) context, a prerequested step to enable emotion-based adaptation during the player-game interaction is the classification of the learner's emotional states into positive vs. negative dimension. Negative emotions mean undesirable emotions that restrain play and have a negative effect on the playing and the learning outcomes. Positive emotions mean desirable emotions that improve play and have a positive effect on the playing and learning outcomes. Therefore, in order to keep the learner engaged, the emotion-based adaptation should be tailored to maximize positive emotions and reduce negative ones. In both education and video game literature, there are many studies about the positive and negative aspects of the emotional states. However, most of the studies on SGs do not take into account the classification of the learner's emotions into a positive and a negative aspect. In order to provide that, this paper contributes a generic classification of learner's emotions in educational SGs. We start by analyzing positive and negative dimension of the learner's (student's) emotions under the educational context. Then, we inspect the learner's (player's) emotional states in the video games context. Finally, we examine emotion in both contexts in order to identify positive and negative emotional states at the learner in the educational SGs context.