I have buy an used iPhone from market after few days it's locked one Apple ID appears on screen at startup I don't know the password of that Apple ID can anyone help me to solve this issue on my iPhone 4

You are the victim of Activation Lock, described here:

http://support.apple.com/kb/HT5818

You must either obtain the permission of the former iPad owner and have them unlock the iPad for you, or your iPad will never be able to be used.

UPDATE - I said "iPad" above because you posted in the iPad forum. If you mean "iPhone", the same is true.

Activation Lock is to prevent selling stolen iPads and iPhones.

Message was edited by: sberman

If you are trying to activate an iPad or iPhone and it is asking for a previous owners Apple ID and password, you have encountered the Activation Lock. This is a security feature that prevents thieves from setting up and using a stolen or lost iPad or iPhone. You have no alternative. No must contact the previous owner to get permission to use the device. If you cannot contact the previous owner return the device to where you bought it and get a refund. You will never be able to activate the device and no one can help you do it.