My wbc count is 6500. can, still my immune system be considered as weak.

Normal...: That is a normal count. I am not sure what you mean by having a weak immune system. This should be looked at though in the context of what your symptoms or illnesses are since this is not a absolute guarantee there are no other problems going on. If you are otherwise healthy this value is normal.

WBC Not Predictive: Is isolated WBC measurement does not predict whether you have a strong or weak immune system. WBC counts can vary naturally over time depending on the situation: illness, stress, etc. If you have concerns about an immune deficiency then I would recommend consultation with an immunologist. If you are otherwise healthy there is no need for further workup.