Given that you are asking about the interview, I suppose that you have successfully gone through the first round of screening. Congratulations!

Coming to the interview, it (generally) would be about the things you have mentioned in your resume (CV), Statement of Purpose and your application.  It is an additional step to check the truthfulness of the details in your application.

Be prepared with:

• All the basics related to your previous coursework, especially anything related to the specialization you are applying for.
• Projects: Be prepared to answer any questions about your previous project. 'Since you have done it yourself, no one knows better about it than you' is the idea behind this testing.
• A general idea about the school you applied for (Their graduate program, the on-going research, professors).
• Questions like 'why did you choose this particular school', 'which professor do you like to work with','what are your research interests'.

Also, you can contact the graduate students from that school to ask what kind of questions to expect in the interview.