Bhingri,
Looks like the beginning of cercospora leaf spot (a fungal issue). I have had some success treating similar issues with a diluted Neem oil spray. Eggplants seem to be relatively tricky plants to grow... we have some that we grew from seed at the nursery I work at and they seem to be pretty prone to insect damage, nutrient deficiency, fungal issues, etc.
If it is a fungal problem, try to minimize the amount of moisture/humidity around your plants, particularly late in the day and into the evening. Also, crowding of foliage (from other eggplants, weeds, or otherwise) can provide ideal conditions for fungus to thrive...
Good luck!
- Meghan
