The current work aims to study the variability in the viscoelastic properties (complex moduli and phase angle) of modified asphalt binder. Viscoelastic properties of asphalt binders are important in characterizing their fundamental and performance-based behaviour. Even with strict quality control, variability occurs within these viscoelastic properties. Asphalt binder is a complex material by itself, which adds uncertainty to its properties. Thus, the uncertainties in asphalt binder properties will produce uncertainties in the pavement response. This present study has focused on investigating the variability within the viscoelastic properties of asphalt binder related to the testing temperature and frequency. In this study, fifteen samples of modified asphalt binder were taken. Using frequency sweep tests, the complex moduli and phase angle values of all fifteen samples were measured. Frequency and temperature master curves were constructed using these measured complex moduli and phase angle values. The variability in complex moduli and phase angle values related to the test temperature and frequency of the asphalt binder was evaluated using various statistical indicators such as coefficient of variation, interquartile range, etc. The results showed significant variability in the complex modulus and phase angle values of all tested asphalt binder samples. Based on the statistical indicators, it was observed that there was higher variability in the complex modulus and phase angle values at extreme frequencies and temperatures. Further, higher variability in the complex modulus and phase angle values was recorded at lower reduced frequencies. Additionally, higher uncertainty was exhibited at higher temperatures for the complex modulus values. In contrast, higher variability in phase angle values were observed at lower temperatures. In comparison between the phase angle and complex modulus values, the phase angle values resulted in higher uncertainty across the temperatures and frequencies.