@joshi_nitish Yes, you are right.
Regular Grammar always generate Regular Language. However, Non-Regular Language may or may not generate Regular Language. In this case a non-regular grammar is generating a regular language.
From the grammar, it is clear that the expression that can be generated is of the form (a(anbn)+ ϵ)a(a+b)* . But I am not able to understand how is it equivalent to a(a+b)*?