Thus far, most electrodes are not wireless capable. This is for many reasons.
First of all, the electrodes need power to stimulate nervous tissue; this would require a battery (which would be bad since it would have to be replaced), or the use of RF telemetry power. By using a wire coil near the implant site and one coil just outside the skin above the internal coil, power can be transferred to the electrodes.
Furthermore, many electrodes record large amounts of data, this would require either a lot of time or a large bandwidth to transfer to an external computer. This computer would be what translates the data into either stimulation signals, sensory signals, or prosthetic movement.
To overcome this problem, researchers are looking at on-board chips to do most of the data processing necessary so that only small amounts of data need to be transferred. Unfortunately, this means the chips will have to be very small and they can only produce a very small amount of heat. Furthermore, the body is a rather hostile environment for electronics.
There has been much research in this area and soon it is likely that most of these implants will be completely wireless.