Avoid page reloaing when click on the asp:Button

I have a web application, one of its Page say Form.aspx has a asp:button control when i click on this button one Popup will come and the pop up also have some asp:button.
[Popup is actually a DIV in the same page , calling it as a popup by jquery "dialog"]
The issue i am facing is when i click on the asp:button in the page as well as in the popup , the whole page is reloading
My requirement is ,
 I have a page Form.aspx and Button1 , when i click on the button - do some server side logic and based on that appropriate popup should come with out reloading the page. Popup also have a buttons say Button2 and Button3 , when i click on this button - do some server side logic and based on that other page should come with out reloading the page.
Thanks in Advance