Can masturbation (whether excessive or normal) affect testosterone level in body?

No: It's "excessive" when you're missing school / work / appointments / parties. Serum testosterone's perhaps low if you're not getting good erections appropriate to your age, and your male hair is falling out. If this is happening, it's not because you're masturbating. Folks who want to control you will tell you that harmless, healthy things are dangerous. Just laugh at these people.