I am actually doing this on a AT89C2051 24PC
This mcu seems to be able to drive 20mA for LEDs and my stepper board is only 10 inches away from the mcu
Do I need a buffer in that case ? Is this buffer only used to increase power ?

If it is an Industrial Application or a Commercial Product I would never use a port pin for driving not even a LED. I have not checked the Electrical specifications of AT89C2051 but 20mA is too much without a buffer. You can easily damage your port pins with this current. I have used stepper motor controllers earlier and my controller needed three signals.
1. ENABLE
2. DIRECTION
3. CLOCK/PULSE

If yours is simillar than use small signal transistors such as BC557 or simillar for buffering your signals. If you need signal lines approx. 8 or more than go for a monolithic buffer. Do Remember to read the buffer datasheet carefully for max. Source and sink currents. and use a buffer that meets your current criterion.

Regards,
Prahlad Purohit