3 stepper motors from 1 board

I'm Akshay and I'm working on a project on controlling 3 stepper motors.

I have ordered an arduino mega 2560 board, along with 3 easy drivers (SparkFun) and 3 5V stepper motors. Can I run all 3 motors with no external supply (i.e just on the supply provided to the board) What will be the results? will the board be overloaded?

That depends on how much current the stepper motors require. If your run your Arduino from USB power you only have about 400 mA left over for all other devices. If you run your Arduino off external power you can only draw about 900 mA before the regulator overheats.

I'm guessing you will need external power.

What exact steppers are you using?

EasyDriver takes 7V to 20V supply, so it'll likely be running from 12V or 18V, anyway you need an external supply as 7V is greater than 5V.

Have you sized your power supply correctly? Which motors? What voltage do you want to use? Bipolar motors are usually rated by current and winding resistance, not voltage.