The comparison the question asks for has, for the most part, never been done. There is no body of rigorous, long-term EEG research that tracks experienced Reiki practitioners over years and sets their brainwave patterns side by side with seasoned meditators. Claims that describe specific differences, more gamma coherence in one group, more alpha dominance in the other, run far ahead of the actual data. They should be read as speculation, not findings.
Where the evidence is genuinely uneven is worth stating clearly. Mindfulness and meditation have been studied with EEG for decades, across many labs and traditions. Some of that work is well known. Long-term meditators have shown increased activity in certain frequency bands, and one widely cited line of research reported unusually strong gamma activity in highly experienced Tibetan Buddhist practitioners. Even within meditation research, results vary by tradition, technique, and how studies are designed, so the picture is real but not tidy. Reiki has nothing comparable. The handful of physiological studies that touch it are small, short, and not built to map years of practice.
That imbalance is the most useful thing to take away. It does not prove Reiki produces no neural changes. It means that no one has gathered the evidence that would let anyone say what those changes are, and any confident description of “Reiki master brainwaves” is filling a gap with imagination.
There are also reasons the two practices resist easy comparison. Meditation is usually a solo, inward activity with a fairly defined attentional target, which makes it more tractable to study. Reiki is typically relational, involving a practitioner and a recipient, and its central claim, the transfer of energy, has not been demonstrated under controlled conditions. An EEG can record a relaxed brain. It cannot confirm that anything is being transmitted.
The state of knowledge here can be summed up in a line. Both practices involve sustained attention and relaxation, and it would not be surprising if both left some mark on the brains of long-term practitioners, since many repeated mental habits do. But the specific longitudinal contrast the title imagines does not yet exist in the literature. The careful reader holds the curiosity and sets aside the invented results, because here the most accurate description of the data is that there is very little of it, and almost none of the kind the question assumes.