A stroke usually brings paralysis or weakness to the lower face, while Bell's palsy usually brings paralysis or weakness to an entire side of your face. Also, Bell's palsy only affects your facial area, while a stroke can target the arm and leg of one side of your body. It is very difficult for most people with active Bell's palsy to wrinkle their foreheads or close their eyes, but most people who have had a stroke can do these things.
Bell's palsy is usually triggered by a virus that inflames a certain facial nerve, while strokes are caused by reduced blood supply to the brain. Lastly, Bell's palsy is not generally life-threatening, while a stroke often is.