We consider the polarization of thermal emission in the near field of various materials, including dielectrics and metallic systems with resonant surface modes. We find that, at thermal equilibrium, the degree of polarization exhibits spatial oscillations with a period of approximately half the optical wavelength, independent of material composition. This result contrasts with that of Setala et al. [Phys. Rev. Lett.88, 123902 (2002)PRLTAO0031-900710.1103/PhysRevLett.88.123902], who find monotonic decay of the degree of polarization for systems in local thermal equilibrium.