Objective: Internally guided actions are defined as being purposeful, self-generated and offering choices between alternatives. Intentional actions are essential to reach individual goals. In previous empirical studies, internally guided actions were predominantly related to functional responses in frontal and parietal areas. The aim of the present study was to distinguish event-related potentials and oscillatory responses of intentional actions and externally guided actions. In addition, we compared neurobiological findings of the decision which action to perform with those referring to the decision whether or not to perform an action. Methods: Twenty-eight subjects participated in adapted go/nogo paradigms, including a voluntary selection condition allowing participants to [1] freely decide whether to press the response button or [2] to decide whether they wanted to press the response button with the right index finger or the left index finger. Results: The reaction times were increased when participants freely decided whether and how they wanted to respond compared to the go condition. Intentional processes were associated with a fronto-centrally located N2 and P3 potential. N2 and P3 amplitudes were increased during intentional actions compared to instructed responses (go). In addition, increased activity in the alpha-, beta- and gamma-frequency range was shown during voluntary behaviour rather than during externally-guided responses. Conclusion: These results may indicate that an additional cognitive process is needed for intentional actions compared to instructed behaviour. However, the neural responses were comparatively independent of the kind of decision that was made (1. decision which action to perform; 2. decision whether or not to perform an action). Significance: The study demonstrates the importance of fronto-central alpha-, beta- and gamma oscillations for voluntary behaviour.