you should never just burn a ouija board. i'm not saying you will release a demon or something, it could just be a toy someone bought and never used, but burning a ouija board that has been used as a tool to communicate with spirits should never be burned because you will unknowingly release a lot of energy, and will receive a lot of negative repercussion because of it.
put it in salt water to purify it of all energy [you could also wash it with vinegar or smudge it with sage among other methods] then burn it. some say you should bless the fire, or make it holy in some way [using a certain type of wood, throwing certain herbs or sea salt onto it] personally, i throw a handful of dried sage on the fire, if you don't want to, don't worry, just be sure to cleanse the board first to make sure theres no energy attached to it.
ouija boards are just tools and a persons belief is what gives it power, but if you just found a random board, better to be safe because the previous owner could of used it.