Broadband high-frequency activity (BHA, 80-150 Hz) represents a crucial analytic signal in human intracranial recordings, with recent studies showing consistent findings of BHA responses to visual stimulation in magnetoencephalography (MEG). However, it is unclear whether BHA indeed represents visual cortex input or primarily indicates internal changes in brain states. Across three studies, we tested whether BHA signals visual input or changes with internal brain states and can serve as a marker for spatial attention. Using simultaneous EEG-MEG recordings in healthy human subjects, we compared MEG-BHA with the EEG-C1 component, representing the initial visual feedforward sweep, to test whether BHA signals visual input. While BHA exhibited similar response characteristics as in invasive studies, only C1 was modulated by contrast. In our second experiment BHA, but not C1, signaled fluctuations in brain states, indexed by mind wandering. Moreover, C1 preceded and predicted BHA modulation, highlighting their different roles. In a subsequent investigation, we tested BHA as an early marker for attentional selection. Attentional selection can be divided into target selection and distractor suppression in a visual search paradigm. We found that BHA distinguishes between targets and distractors and preceded amplitude modulation of low-frequency components of target enhancement and distractor suppression. BHA responses predicted performance earlier and more accurately. In summary, our findings suggest that BHA indicates internal brain state changes in human visual cortex.