I am a 21 year old male. I have frequent arousals everyday, especially when I am in the locker room or shower, all time erection annoys me. How can I stop being sexually aroused and prevent erection at sometimes?

Think of math? It is often a autonomic reaction. You see something arousing, or even just think of something arousing, and you get an erection. This goes away in time, but I would ensure you have a towel around.

I want to suggest posting this in a medical section. Getting aroused at something arousing is normal. Becoming aroused all the time for no apparent reason is a bit odd.

Are you aroused more in the morning, afternoon, evening? All day?
This may be something to speak to your doctor about.