if i scroll down to last post and click like button(Like button is provided for every post). it goes to top of page.
Why such implementation? For 'Like' pass on the request asynchronously. Right now, when you clicked the link, a postback happened and thus the top of page.
If you want to stick to current implementation (which is actual issue), try:
Maintain Scroll Position on Postback in ASP.NET 2.0[
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