Understanding the states of learners at a lecture is useful for improving the quality of the lecture. A video camera with an infrared sensor Kinect has been widely studied and proved to be useful for some kinds of activity recognition. However, learners in a lecture usually do not act with large moving. This paper evaluates Kinect for use of activity recognition of learners. The authors considered four activities for detecting states of a learner, and collected the data with the activities by a Kinect. They applied K-nearest neighbor algorithm to the collected data and obtained the accuracy 0.936 of the activity recognition. The result shows that Kinect is applicable also to the activity recognition of learners in a lecture.