Permanent deformation is one of the major pavement distresses in flexible pavements. Several studies have shown that asphalt-rubber (AR) mixtures are less susceptible to high temperature rutting, fatigue cracking, and low temperature thermal cracking distresses based on the field performance characteristics. Although there are many different experiments to characterize rutting, there is not a single parameter that can completely explain the rutting phenomenon from viscoelastic perspective. Thus, the main objective of this study was to evaluate permanent deformation characteristics of the asphalt-rubber mixtures in terms of stiffness parameter (E*/sinϕ) using two different laboratory test procedures. During the process of study, two different rutting parameters were obtained and assessed using the following experiments: (a) E* dynamic modulus test at five temperatures and ten frequencies; (b) Repeated Load Permanent Deformation Flow Number test at 54 oC. The materials used in the study encompasses Bituminous Concrete (BC-1 type) gradation with aggregate size of 19 mm based on Indian specifications; two different binder grades, namely, crumb-rubber modified binder (CRMB-60) and virgin viscosity graded bitumen (VG-30). The results of this study clearly indicated that modified asphalt mix would perform superior compared to the conventional mix. A good correlation between FN and E*/sinϕ with R2 of 0.751 was also obtained at 54 °C and 10 Hz, thus recommending E*/sinϕ stiffness parameter as a rational rutting parameter to assess mixture rutting characteristics.