Expungement laws vary from State to State. You should contact a criminal defense attorney who practices in the State where you were convicted to find out whether you qualify for expungement.
Even if the record is expunged, federal law enforcement officers may be able to determine whether you had been arrested. Definitely consult with an experienced criminal defense attorney in your state but be prepared to have to come clean with the feds. Remember that lying to a federal officer is a felony, which includes failing to disclose a material fact. See 18 USC 1001.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.