The effect of reinforcement clustering on the steady-state creep behaviors of unidirectional SiC whisker reinforced aluminum matrix composite was investigated using finite element models with two different microstructures: Homogeneous microstructure was made up of a random dispersion of whiskers and the heterogeneous (clustered) one was idealized using hierarchical multiscale technique with 2D microstructure image of this material. Based on the numerical results, a possible mechanism for the ‘anomalously high’ creep stress exponent was proposed in the light of current knowledge.