I have recently resigned from a firm with 6 months experience for the designation Technical support . I resigned this job as it was too technical for me as my background career doesnt suit for IT side and I find it difficult to overcome the pressure and additionally they asked to sign up a bond for 2 yrs ..
Suggest me to answer in interview on "why you resigned from your previous job ??"

Do I understand you
Do I understand you correctly: you quit your job with no other position lined up because you felt you weren't qualified to do that job?
If that's correct, there's no good answer unless you can follow it with how you learned that was a bad idea and you would never do it again.
Here is what I would say...
I would be honest. You were working there and realized it was not working out and they wanted you to take on a 2 year commitment.
This is can actually be a good thing. Some people would have stayed for the security, even though the position was not a good fit. 2 years is pretty long commitment, depending upon your circumstance. As a manager, I would much rather have someone leave because they are not a good fit, then stay.
There can be many good reasons to stay in a poor fit role, at least temporarily, but those are all about what you will gain from that time.
Getting real with yourself...
The brings to mind two quotes from Susan Scott's book, "Fierce Conversations.
Page 62: "If you want to see someone in real pain, watch someone who knows who he is and defaults on it on a regular basis."
Page 63: "It may be time to screw your courage to the sticking-place and fire yourself. Make yourself available to industry. Make yourself available to whatever is out there with your name on it."
So much for the philosophy, now for the actionable advice...
Getting Fired - Part 1
Getting Fired - Part 2
Good luck!
--Michael