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As a promising thermoelectric material, BiCuSeO is of great interest for energy conversion. A higher figure of merit in n-type BiCuSeO than that in the p-type was predicted from theory, suggesting a need of in-depth investigations on the doping effects. In this work, the influences of group IV elements (Si, Ge, Sn, and Pb) on the electronic structures of BiCuSeO are studied from first principles. Despite the similar electronegativities of the group IV elements, Si is found to be an n-type dopant, being distinctly different from Ge, Sn, and Pb, which exhibit typical p-type behaviors. Detailed analysis on the doping effects is performed based on a recently developed band unfolding technique. Furthermore, Si-doped BiCuSeO is shown to have a higher power factor than p-type BiCuSeO from the Boltzmann transport theory.