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 midterm elections are federal elections that occur every two years and include all 435 seats in the US House of Representatives along with one-third of the US Senate seats. Your vote is crucial to determine control of Congress!