Mechanical and tribological properties of polyetheretherketone (PEEK) based nanocomposites filled with nanoparticles of i) copper (Cu), ii) brass (Cu-Zn), iii) silicon dioxide (SiO2) and iv) copper ferrite (CuFe2O4) at tribotesting against metal and ceramic counterparts were studied. It is shown that at nanofillers content 0.3 wt. % the mechanical properties of the composites (elastic modulus, tensile strength) increased by 10-12 %, while the elongation at break decreased by 5-7 %. For most of the nanofillers used the wear rate of the composites increased at testing in metal- polymer tribological conjugation, while it always decreased at testing against ceramic counterpart. It is shown that nanofillers ensured dispersion hardening and did not act as a solid lubricant in the composites based on the high-strength PEEK matrix. The increasing wear resistance in metal-polymer tribological conjugation can be attained through the formation of a polymer transfer film on the steel counterpart which protects both components of the friction pair from intensive wear.