[Purpose] Among the physical therapeutic procedures to decrease pain, there is transcutaneous electrical neural stimulation (TENS). There is no consensus about its efficacy for oncological patients, especially for post-mastectomy pain and eletrocortical changes in somatosensory areas. The aim of this study was to analyze acute electrocortical changes after TENS treatment of patients with intercostobrachial post mastectomy pain. [Subjects] Eighteen patients were divided into acupuncture (A) and burst (B) group. [Methods] In this pre and post-intervention study each group was measured for EEG analysis in absulte power in alpha band (8-14 Hz). Outcomes variables were the alpha waveband in the sensorymotor cortex and pain pre-and-post TENS intervention. Data were analyzed using ANOVA to compare times (rest, 10 and 15 min), group and electrodes. Pain was analyzed using percentual pain evaluation (PPE) in both groups. [Results] Outcomes indicate main effects of time and electrodes because of slow (8-10 Hz) and fast alpha (10-12 Hz) wavebands decreased. PPE reduced 88.4% in A and 66.3% in G. [Conclusion] TENS promoted electrical modification in the parietal region and a decrease in pain. Future studies should investigate other wave must be proposed for other bands and use different methods of EEG analysis to elucidate the actual mechanisms behind the efficacy of TENS treatment.