Hello Harsha
By design, BGP is made so that each router belongs to a single AS. But this doesn’t limit its functionality. You can still peer with routers from multiple AS as well as to routers in the same AS. There is however a way to allow a router to appear to neighbors to be a member of a second AS using what is called the Local-AS feature. This is usually done for migrations when moving from one ISP to another, or from one MPLS provider to another, and is usually provided as a temporary solution during the migration process.
BGP is designed to function with only a single AS assigned to each router.
I hope this has been helpful!
Laz