Not at all. Helmets for different activities are optimized to different crash scenarios to prevent different kinds of injuries. Motorcycle helmets are designed mainly to prevent skull fractures in high speed crashes; the shells are very hard, and the liners are highly resilient but very stiff. Bike (and ski & skate) helmets are designed for lower speed impacts, with the goal of preventing concussions; they have shells that shatter/break, and liners that break or deform to absorb energy. A motorcycle helmet isn't going to do much to prevent or ameliorate a concussion. If you want a more complete explanation of these things, helmets.org is a good resource.