In this work we examined how the variability in the brain morphology and the tissue properties affect the assessment of the homogeneous human brain exposed to high frequency electromagnetic (EM) field. Using the deterministic EM-thermal modeling and the stochastic theoretical basis we have studied the effects of these uncertainties on the maximum induced electric field, maximum local Specific Absorption Rate (SAR), average SAR, maximum temperature and the maximum temperature increase, respectively. The results show a good convergence of stochastic technique and an assessment of mean and variance of outputs for the incident plane wave of 900 MHz.