The purpose of this study is to evaluate the accuracy of monocular marker-less 3D motion capture based on camera location and plane by comparing the range of motion (ROM) angles of the right arm joints using a marker-based 3D motion capture system. The ROM for each degree of freedom of the right-side shoulder and elbow joints was simultaneously measured using a marker-based 3D motion capture system and the monocular markerless 3D motion capture model, MediaPipe. The camera location and plane were considered as independent variables. As a dependent variable, this study analyzed the mean absolute error from the angles measured by between the systems and performed a two-way ANOVA. The results showed that the camera location and plane had a significant effect on the accuracy of marker-less motion capture for each joint. The accuracy of the shoulder was generally higher under the experimental conditions of 315°, frontal at 0°, 180°, and sagittal at 315°. The accuracy of the elbow was higher under the experimental conditions of 90° and 135°. This study found that positioning the camera diagonally relative to the body yielded higher accuracy. Therefore, this study suggested that the camera location should be positioned at 135° and 315° for monocular 3D markerless motion capture of the arm.