Yes! All U.S. citizens living outside the U.S. may vote in federal elections for U.S. Senate and U.S. House of Representatives as well as President. See the answer to FAQ #1 (“I Live Outside The U.S., Am I Eligible To Vote In U.S. Elections?”)
The entire membership of the U.S. House of Representatives is up for election in midterm elections, as is one-third of the U.S. Senate. Your vote is crucial to determine control of Congress!