Both EEG and fMRI show characteristic fluctuations over time in the resting state. The functional significance of these fluctuations still unclear. By combining both methods and allowing time lags of up to 10.5 s between the two modalities, we show that functional MRI increases commonly precede EEG power increases by seconds. This indicates that at least one common mechanism connecting fMRI and EEG changes is much slower than expected with direct neural transmission.