I believe it depends on the state/city laws, but in Ohio, any deck/porch that's 24" above ground / grade require railing. Ironically, if you pour dirt around the deck and therefore raise the grade by, say 6", then you don't need it since from the bottom of the deck to the top of the grade is 18" (24-6). You probably don't need it, but check with your city.

National code says if you have > 3 stairs you need a railing. I'm not sure by your description of "3 risers" if you've got 3 or 4 steps, though. If you only make 3 steps between the deck and the ground, that's almost 10" risers, which is way too steep.

Here's a photo of stairs that don't need railings. If you've got one more step than this, then you need a railing.