The viscoelastic behaviour of gum and a highly filled ethylene-propylene terpolymer (automotive windowseal component) at 138 parts carbon black loading was investigated using a dynamic mechanical analyser over a wide range of time, temperature, strain and frequency. The tensile stress relaxation and recovery results of the gum system show time-dependent but strain-invariant behaviour, whereas the filled system shows both strain and time dependence. The relaxation time spectrum of the filled system reveals nonlinear viscoelastic behaviour. The networks of carbon black formed at such a high loading contribute significantly to the relaxation process. The 3D plot of tensile modulus as a function of time and temperature for both the systems follow a similar trend, and even for short-time testing the highly filled system appears to be time-temperature superposable.