The present report examines a possible co-maturation pattern between different frequency ranges on the spontaneous electroencephalogram (EEG) during development in childhood, adolescence and young adulthood. One hundred and sixty-seven subjects, between 6 and 26 years old were recorded during 3 min of spontaneous EEG. The power spectral density (PSD) logarithm was computed. There was a decrease in all frequency band ranges between 1 and 46 Hz. Correlation matrices for these frequencies were computed. A general trend of PSD correlation with neighboring frequencies was obtained. Furthermore, there was a high correlation during development between theta and beta ranges, and between high-beta and gamma frequency ranges. The correlation of theta versus beta was particularly high between the anterior and posterior electrode sites. Principal component analysis allowed the extraction of six components explaining the variance associated with the delta, theta, alpha, low-beta, high-beta and gamma ranges. Interestingly, the component explaining the theta rhythm also explained a fraction of the low-beta rhythm during development. The results suggest a pattern of co-maturation in the PSD of spontaneous EEG between theta and low-beta, and between high-beta and gamma, which would be due to the maturation of neural tissue underlying the sources of different frequencies. The possible functional role of theta-beta co-maturation in fronto-parietal electrode sites is suggested.