Question: I was reading about CMS and ERP. And got confused at this point that whether a system can both be an ERP and a CMS? is it possible?

Answer: 
Sure - you can program whatever you like. Whether it makes any sense is a different question.

As for whether having an ERP/CMS hybrid makes sense or already exists - I don't think so. There are some vague similarities and overlaps in that both will typically allow you to define your own entities with fields ("document types" in a CMS, "business objects" in an ERP) and present a web interface for data entry and publishing, but at heart they have completely different purposes.
In most cases this would not make very much sense,ERP system generally use in business management.An CMS able to edit not only content but the entire design can be edited.Information that is not important for business prospective are edited by CMS.