Objective: Neurofeedback has been proposed as an effective alternative for pharmacological treatment in children with attention-deficit/hyperactivity disorder (ADHD), with potentially long-term and delayed benefits. However, the specificity of such long-term behavioral improvements remains inconclusive and therefore additional research into the neurophysiological effects of neurofeedback is needed. We compared long-term effects of theta/beta neurofeedback (NFB) to methylphenidate (MPH) and physical activity (PA, semi-active control intervention) on electroencephalogram (EEG) power spectra. Based on the vigilance stabilization model, we hypothesized further reductions in theta and alpha power in the NFB compared to the control groups. Method: EEG power spectra (theta, alpha and beta) during resting and task conditions were recorded at pre-, post-intervention and 6-months follow-up in 67 children, aged 7–13 (NFB: n = 24, MPH: n = 23, or PA: n = 20). Results: Analyses revealed no power spectra differences at follow-up between MPH and NFB (range p = .165–.905) and PA and NFB (range p = .172–.822). Conclusions: No evidence was found for the specificity of theta/beta NFB at follow-up. Significance: This was the first study into long-term neurophysiological effects of theta/beta NFB. Future studies are encouraged to explore both specific and non-specific mechanisms of NFB. Clinical trials registration: Train Your Brain? Exercise and neurofeedback intervention for ADHD, https://clinicaltrials.gov/show/NCT01363544, Ref. No. NCT01363544.