Today people are developing technology to interface directly with the brain. One of the more safe ones (besides just a keyboard and mouse) is EEG (ElectroEncephaloGram). With EEG electrical probes are attached to the head on the surface. These connections are wired to a pre-amplifier or instrument amplifier, digitized and feed into a PC or Mac computer for analysis.

Several very low frequency brain waves have been discovered. The waves are actually radio waves (electro-magnetic) but the magnetic component is so small that just the electrical component is picked up.

Here is a few great articles:
Brain Computer Interfaces
Interface Tech for the Brain