2000 accent manual trans problem
 

I have a 2000 accent 5 speed manual, with 35000 miles on it. I purchased it last week and put about 200 miles on it. While on the highway today at 65 mph it just came out of 5th gear. It went right in again and was fine. I took the car out tonight and it did it 2 more times. Any idea of what it could be.