If you don't have the Passcode, you need to restore the device from the computer it was last synced with. There is no "default" passcode.
Follow the instructions for putting the device in recovery mode > iPhone and iPod touch: Unable to update or restore
There is no default passcode for an iPad and while the article that Carolyn has referenced will put you on the right track, the bigger concern for me is that you don't know how a passcode was entered on your device.
Is you iPad employer owned? If so and if you have an Exchange email account, quite often the administrator will place a
passcode on the device but I should think that they would make you aware of that.
Is it possible that a friend or family member entered the code and you are unaware of that? It has happened to other users in the past.
Was this a brand new out of the box iPad - not a store demo?
First of all thanks for the reply.. secondly, it's not employer owned iPad, but yesterday I have added our employer outlook e-mail account, and after that usage it started asking me the password. I think that is may be the cause here.
Moreover, I bought the iPad 3 days back I have not synched it with iTunes yet. So how can I recover it now?
I believe then, that you need to talk to your employer and he/she will have to provide the passcode for you. I'm not really sure how that works, but if you are using your company email account on the device, it must be set up so that you need the passcode to unlock the device.
I would not restore it, to unlock it, without your employer's OK - if you are going to use your company email account the device.