http://www.licindia.in/nri_centre.htm
NRI should not be a green card holder. He/She should not have applied for or planning to apply in the near future for acquiring citizenship of his /her present country of residence or any other country.
It is clarified that People of Indian Origin having foreign nationality and residing in foreign countries (PIO) are not considered as NRIs for the purpose of allowing insurance. Rules applicable to PIOs are given in the last paragraph.
In short, if you are NRI and are not going to apply for Green Card than you can buy, otherwise not.