That would be very complicated, but essentially you could. You can already use electrodes to stimulate muscles for healthcare, re-education after surgery, or for bodybuilding. What you're suggesting through the brain is perhaps technically possible but impossible with modern science. Better to target motor neurons. Of course if you want it to make a normal, natural movement, you'll need to do the brain's work, and send just the correct amount of energy at just the correct frequency, which is an action potential. Ideally you'd find a way to stimulate the nerves directly like the brain or other nerves would rather than with electricity, you'd use neurotransmitters, but at this point you're just replacing the brain with a computer. This is complicated but not technically impossible. We just never made and probably never will make something that does that, and if we did it would take very, very long and doubtlessly we'd learn a lot of new things about nerves along the way that would be roadblocks for a time