This is a difficult question to answer because it depends on a lot of factors, such as your GPA, what you're studying, what research experience you have, and so on. The best way to find out is to consult the website of the graduate school you're interested in and look at the requirements for admission.
For example, here are the requirements for admission to the MIT Department of Electrical Engineering and Computer Science:
As you can see, they vary depending on whether you're applying for the Master's program or the PhD program. In general, though, getting into a graduate program at MIT is extremely competitive.