We constructed a computational model of the driver’s brain for steering tasks using the active inference framework, grounded in the free energy principle—a theory from computational neuroscience. This model enables quantitative estimation of how accurately the brain learns vehicle dynamics and performs appropriate steering, using a measure called variational free energy. Through driving simulator experiments, we observed strong correlations between variational free energy and both expert drivers’ subjective “as-intended” scores and general participants’ objective control performance. These results suggest that variational free energy provides a promising quantitative metric for evaluating whether a vehicle behaves “as-intended.”