Is it normal to have voices in your brain?

I have voices that I do not physically hear but hear like thoughts. Like when you talk to yourself in your brain. But, these aren't my thoughts. Or I don't know if they are. Sometimes they are sporadic and mean. Like yesterday my mom was bringing me something and dropped it. I honestly don't care but a voice in my head was screaming stuff like "Kill that fucking weak bitch." This happens frequently. Sometimes the thoughts are different. Like some scream at me to do things. If I didn't have them, I would probably get nothing done, but they scare me sometimes. Not all are bad. Others help me plan and succeed in academics. Is this normal???