IN which direction and at what velocity? Vertically and stationary, it is whatever they weigh. Under any other condition is is a function of mass and velocity.
Yeah, F=mA, but keep your units consistent. http://en.wikipedia.org/wiki/Newton's_laws_of_motion
If A is the accel. of gravity at 32.2 ft/seconds squared and F = 161 pounds = a person's weight, that person's mass in "slugs" is 5.