Can healthy people get false positive elisa hiv test? if so why?

Yes, it is possible: Some people may have a biologically false-positive test for hiv, when tested by elisa. Such people usually have a negative or indeterminate confirmatory test, the western blot. That usually happens because of some antibodies that were directed against other organisms recognizing part of hiv. If there is any question, a qualitative HIV dna pcr may put the question to rest.