How do I know if I am capable of an advanced degree?

Hello I am a junior EE student at a state college in the northeast. I have interest in graduate school, but I am not sure if I am even capable of this. I was never the most amazing student in school although in high school I almost never tried. In college I have tried quite a bit harder but generally earn average grades. Is it difficult for such a person to continue on to a masters degree? I don't have that many responsibilities outside of school although I work part time. If I was going to do a masters I would continue at the same school I am at now and would (hopefully) work as a TA to get my tuition off. I don't have any experience in a leadership role and have only worked pretty menial jobs (janitor, warehouse, etc). Can an average student make it in a master's program? Over the years I have discovered I am very interested in electromagnetics, signal processing, and electronics although like I said before I was never the greatest at tests.

​

Most of the grad students I see are the typical 3.5+ GPA students who knew they were destined for advanced degrees, whereas I am just an average guy who didn't even think about going to college until a year after graduation (I'm 21 now). I'd like to know everyone's opinions. I am not hugely confident about school but I do like to learn and would continue learning on my own even after graduation