  We show that some composite pulses widely employed in NMR experiments are
regarded as non-adiabatic geometric quantum gates with Aharanov-Anandan phases.
Thus, we reveal the presence of a fundamental issue on quantum mechanics behind
the traditional technique of the composite pulses. To examine the robustness of
such composite pulses against fluctuations, we present a practical noise model
in a two-level system. Then, we find that the composite pulses possesses purely
geometrical nature even under a specific type of fluctuations.
