To explore the effects of acupuncture stimulation on brain activities, an experiment is designed that acupunctures at Zusanli point of the right leg are performed at four different frequencies to obtain electroencephalograph (EEG) signals. For the first time the complexity parameter of EEG is extracted by order recurrence plot and correlation dimension method, which reflects the functional state of the brain under acupuncture. The effects of acupuncture on the functional region of brain and correlation among different acupuncture frequencies and the complexity of EEG are investigated. The results show that the complexity of EEG during acupuncture is higher than that before acupuncture and especially during acupuncture at a frequency of 100 times/min. Furthermore, the determinism (DET) extracted from EEG signals of electrodes FP2, F7 and T3 can be used as a characteristic parameter of distinction between the state during acupuncture and the state before acupuncture.