If by brake you mean a way if increasing resistance, there is. A mechanical brake isn't practical because couldn't dissipate heat fast enough so after a short while it would get unacceptably hot. (Imagine riding all day dragging your brakes). Instead trainers create resistance wither through magnetism, a fan, an impeller moving fluid, etc. All trainers have resistance units, and each method of resistance has advantages and drawbacks.
Some treiners allow you to change the level or resistance, while others have reisistance that increases with speed (a power curve) better simulating the natural resistance of outdoor riding.
BTW- if you do buy a trainer, invest in some training videos, or at least some other form of entertainment. Stationary training can be incredibly boring otherwise.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.