We investigate the optical polarization properties of high-energy BL Lac objects using data from the RoboPol blazar monitoring program and the Nordic Optical Telescope. We wish to understand if there are differences between the BL Lac objects that have been detected with the current-generation TeV instruments and those objects that have not yet been detected. We used a maximum-likelihood method to investigate the optical polarization fraction and its variability in these sources. In order to study the polarization position angle variability, we calculated the time derivative of the electric vector position angle (EVPA) change. We also studied the spread in the Stokes Q/I-U/I plane and rotations in the polarization plane.