Recent transport, specific heat and magnetization measurements indicated that the Heusler-type compound is a candidate for a 3d heavy-fermion system. As a first step towards a detailed theoretical understanding of the observed anomalous electronic properties of this compound, we have performed first-principles electronic structure and total energy calculations for and . The calculated lattice constants and magnetic moments are in good agreement with experiments. Remarkably, we find that, unlike , Heusler-type is a nonmagnetic semimetal with a narrow pseudogap at the Fermi level. Furthermore, our calculations suggest that the observed large enhancement of electronic specific heat coefficient is largely caused by the mechanisms such as spin-fluctuations rather than electron - phonon coupling in . The relations between the existence of the Fermi surface and negative temperature dependence of the low-temperature electrical resistivity in are discussed and further experimental and theoretical work is suggested.