I'm staying in usa on B1/B2 Visa. i want to get a Tax ID number.

It depends upon whether the DHS/CBP has reason to believe that you are improperly living and working in the U.S. If you are simply opening up a bank account and transferring funds to maintain yourself in the U.S. then this should be acceptable. By law, you are supposed to be visiting the U.S., not employed with a U.S. entity, where you enter in B-2 status. For more information, I recommend an appointment or teleconference experienced immigration attorney. Some misunderstand B-1 visa status and how it is meant to work. A significant CBP oversight may occur at an airport, where there is any confusion. The above information and below link are general information and do not create an attorney-client relationship.