  We use the method of the exact renormalization group to study the
renormalization group flows of an O(N) invariant Yukawa model in three
dimensional Euclidean space consisting of one real scalar and N real spinor
fields. We obtain a phase structure similar to that of the N-vector model with
cubic anisotropy, possessing a region of parameters exhibiting a first order
transition. The particular case with one real fermion (N=1) belongs to the same
universality class as the Wess-Zumino model with one supersymmetry. For the
critical exponents of the Wilson-Fisher type fixed points, our 1-loop
approximations are generally consistent with the results of previous studies.
