A very rapid swing in the polarization position angle (PA) in the optical region was observed in blazar OJ 287 during one night of our five nights UBVRI photopolarimetric monitoring in January 1991 with the Nordic Optical Telescope. During this PA swing the flux increased ~40% in five hours, while the polarization level was very stable and quite low. This is the fastest large PA swing and one of the fastest changes in the flux ever observed in any blazar. We find it difficult to explain these observations using the standard two-component or shock in the jet model. We have considered two kinds of interpretations based on relativistic beaming effects and flaring accretion disk.