Myoclonic seizures are defined as generalized seizures according to the classification of seizure by the International League Against Epilepsy (ILAE). The pathogenesis of myoclonic seizures is not yet clear. There are very few studies on the focal surgical treatment of myoclonic seizures. The aim of this study is to investigate the characteristics of myoclonic seizure onset in different bands of the intracranial electroencephalogram (EEG) and their dynamic changes in temporal and spatial evolution. We studied four patients with myoclonic seizures who were under the focal resection of the epileptogenic zone. We retrospectively analyzed the semiology, electrocorticogram (ECoG) and imaging data of these patients, and conducted time-frequency analysis of broadband ECoG activity. We found that myoclonic seizures without clinical lateralizing signs could be improved by the resection of the epileptogenic zone. The ECoG power in different frequency bands increased to a peak at 0.5 s before the clinical seizure onset and decreased quickly afterwards. The power of alpha activity was highest during the preictal and ictal periods. The central zone had higher power than the epileptogenic zone in all frequency bands during the preictal period, but this difference was not statistically significant. Our results suggest that myoclonic seizures in some patients might have a focal origination, with a fast bilateral propagating network in all frequency bands, especially the alpha band.