Motor system excitability was tested by transcranial magnetic stimulation (TMS), and F-wave and H-reflex evaluation in different action observation tasks. Our aim was to investigate the effects produced by self- versus non-self-hand movement observation (MO). No significant differences were found between the self- and non-self-conditions. Movement observation significantly modulated motor cortex excitability, producing an increase in the amplitude of motor evoked potentials (MEPs) with a single magnetic pulse and a reduction in intracortical inhibition (ICI) with paired-pulse stimulation. No significant changes were found in motor cortex excitability during the observation of geometric objects. Motor imagery produced similar effects to those of action observation; no significant differences in modulation of motor system excitability between motor imagery and action observation were found in those muscles involved in actual motor execution. No significant effect on spinal excitability was found in any of the test conditions.