Yes, it is mandatory to file returns if your income exceeds the basic tax exemption limit, which is Rs 2.5 lakh for those below 60 years of age. Irrespective of your income, you must file returns if your foreign travel expenses in a financial year exceeded Rs 2 lakh or your electricity bill amount crossed Rs 1 lakh. The same is the case if you have foreign income or assets. Then, there are other conditions, too, that make filing of returns mandatory, irrespective of your income.