Sir/mam,I am a 2nd yr student of the bachelor in computer science(bcs).am I eligible to appear for gre?I will be completing my 3 yrs. Graduation in2014.

I don't know much about the GRE but I do know their website is probably able to answer all of your questions: GRE

If it's like the MCAT you're able to take it whenever you want, so long as you feel prepared.