I determine the critical behavior of a nonequilibrium three-dimensional lattice model exhibiting a phase transition to an absorbing state. I study the model in the vicinity of the critical point, and in the subcritical region, via time-dependent Monte Carlo simulations. The method used in the subcritical region is very efficient. The results for the directly measured critical exponents, =1.11±0.01, =0.114±0.004, and z=1.052±0.003, are consistent with those of directed percolation. =0.732±0.004 is obtained from the hyperscaling relation 4+2=dz, and =0.813±0.011 from =. These results are the most precise so far for a three-dimensional model with directed percolation critical behavior.