Foreign nationals are generally allowed to present at professional conferences/festival in “visitor” status, provided they receive no remuneration from a U.S. source other than that which covers reasonable expenses.1 This means that if you are eligible to enter the U.S. under the Visa Waiver Program (“ESTA”) that is sufficient. If you are not eligible to enter the U.S. under the Visa Waiver Program (“ESTA”), you will probably need a B-1 visa.
1 See 9 FAM 402.2-5(B) and 9 FAM 402.2-5(F)(1)