Blue cheese should not normally make your tongue numb.
However if your tongue does go numb and tingle as a result of eating blue cheese it's likely cause you're allergic to the blue cheese and have a food allergy.
I would let a doctor know about the tongue going numb and if it only happens when you eat blue cheese and not other cheeses then it's likely the blue cheese that you're allergic too.
I would advise to stop eating the blue cheese until you get tested by a doctor because the allergy to the blue cheese could be potentially fatal if you continue eating the blue cheese.
Basically it's probably a small histamine reaction which also means you're allergic to the blue cheese.
Blue cheese should not cause most peoples tongues to go numb but it would be a good idea to let your doctor know about it just to be safe.