This paper evaluates the role of the air voids (AV) variability of asphalt mixtures on the thermo-mechanical response of asphalt courses. The methodology presented combines finite element (FE) modelling with a stochastic technique called random fields. This technique is used to generate probable spatial AV distributions in the geometry of compacted asphalt courses. Thus, several asphalt layers with AV contents varying in space were implemented in FEs, and a thermal diffusion process followed by a mechanical loading scheme was simulated. The mechanical response of the asphalt course was made dependent on both the specific AV content and temperature at each point within the layer. It was found that the quality of the compaction process, represented by the dispersion of the AV, strongly impacts the thermal diffusion processes and the uncertainty of the mechanical response of asphalt courses.