The planetary roller screw mechanism (PRSM), with high load-bearing capacity, long service life, and high precision, is the new type of thread-pairs transmission mechanism, which is widely used in the weapon system and industrial robot. The friction force is caused by the sliding motion, and the geometrical errors change the contact characteristics and rolling-sliding motion, such as eccentric errors. However, the friction characteristics of PRSM with the eccentric errors have been unclear. Hence, this work investigates the friction characteristics of PRSM with the eccentric errors. The sliding friction coefficient of thread pairs is determined based on the equivalent friction test. The sliding friction value and direction of thread pairs on screw-roller (SR) side with the eccentric errors of nut and screw are analyzed. It is found that the eccentric errors cause the periodic variations of the friction force and direction. The eccentric errors of nut and screw have the combined effects on the sliding friction force and friction torque of thread pairs on the SR side.