Yes and no. I have no idea what species you are growing, but B. hirta is the major species grown for seeds used in condiments. B. juncea and B. rapa var perviridis are most commonly grown for greens. The seeds of these will not hurt you, but will not have the flavor of the B. hirta species.

Here is a link that might be useful: Mustard

But nevertheless, pretty mustardy.....

Some farmers use mustard plants as a green manure. When they plow them under, they may miss some (like along the fence lines) that flower and go to seed. The birds eat them, moisten and soften them in their digestive tract, and then drop them on your soil with a little blob of manure, and they sprout.

If you deliberately want to grow condiment-type mustard, go to a grocery that sells bulk spices (Fred Meyer/Kroger) or a health food store and buy a spoonful of seed. Most of these natural seeds will sprout. Then you'll know what you've got.

Sue

Here is a link that might be useful: Mustard- growing & using

White mustard (colored yellow) comes from the mustard plant Sinapis alba. Mustard greens are usually Brassica juncea. Black mustard is usually Brassica nigra (popular in Indian cooking). The seed of any of these, sometimes colored, may be sold as 'mustard seed' spice.