Rebate on agriculture income in itr2

Hi, I have STCG of Rs. 12520 in shares. So thats a tax of Rs.1878. Now while filing returns, under Part B -TTI (1 c) of ITR2, "Rebate on agriculture income [applicable is (12-13) of part b-ti exceeds maximum amount not chargeable to tax]".. I am getting a rebate of Rs. 1878, I don't know what it is and why am I getting a rebate. Please clarify this.