The stability of quantum computating of the kicked Harper model with various perturbations is investigated. Above a certain threshold of the imperfections, quantum chaos sets in. The effects of the noise errors and the static imperfections on the quantum computation are analyzed by comparing the statistical ergodic properties and the Husimi functions of the perturbed eigenstates with the ideal eigenstates of the Floquet operator. It is shown that the fidelity decay with static imperfections is exponential while it is Gaussian with noise errors. The time scales of reliable computation with these perturbations are obtained through numerical simulations. Due to the errors in classical computation the distance of two initial states increases exponentially, while the stability of quantum computation is independent of the integrable or chaotic nature of the underlying dynamics.