In this paper, we propose a robust transmit beampattern design for multiple-input multiple-output (MIMO) radar systems. The objective considered here is minimization of the beampattern sidelobes, subject to constraints on the transmit power where the waveform co-variance matrix is the optimization variable. Motivated by the fact that the steering vectors are subject to uncertainties in practice, we propose a worst-case robust beampattern design where the uncertainties are parameterized by a deterministic set. We show that the resulting non-convex maximin problem can be translated into a convex problem. We numerically illustrate that the steering vector uncertainty yields a severe degradation in the array performance, i.e., the transmit beampattern. Also, we show that the proposed robust design improves the transmit beampattern by reducing the worst case sidelobe peak levels.