We study the vacuum stability of a model of massless scalar and fermionic fields minimally coupled to a Chern-Simons field. The classical Lagrangian involves only dimensionless parameters, and the model can be thought of as a (2+1)-dimensional analogue of the Coleman-Weinberg model. By calculating the effective potential, we show that dynamical symmetry breakdown occurs in the two-loop approximation. The vacuum becomes asymmetric and mass generation for the boson and fermion fields takes place. Renormalization group arguments are used to clarify some aspects of the solution.