My ncs test result normal, hbsag result negative, no diabetes. no chronic pain condition. however, i still have burning sensation in my feet. why?

Many causes : Burning in feet is often due to peripheral neuropathy. EMG/NCS are often negative. Chronic kidney disease can be a cause. Make sure they rule out myeloma, B12 or folate deficiency.. other causes Include chronic inflammation from parasites, asthma, etc.. Once they rule out a known disease, there are nutritional approaches that can help nerves heal. Look up "functional medicine".

Other history: Given you have had a number of specific diagnostic tests, you may need to go to a specialist to have more detailed evaluations of the issue. Often times patients with certain types of neuropathy (eg small fiber neuropathy) will have normal electrodiagnostics but need additional tests to make the diagnosis. Suggest you obtain a second opinion from a specialist in either neuromuscular disease.