Sometimes it is needed to clear (remove, erase) the Mbr. Of course, you must first know where it is. Here is a simple workflow to erase it under Linux

All of the following must be executed as root, so sudo bash.
 
After Mbr is lost you will not be able to boot, so make sure that you know exactly what to do next, like installing a clean boot manager (Lilo, Grub, etc).

1

Locate MBR

Where is your MBR (find Boot Device)? fdisk -l

Normally it is one of:

1. /dev/hda if your have IDE disk
2. /dev/sda if your use SCSI disk

 
Of course, your case may be different.

2

Clear MBR

Clear with:
dd if=/dev/zero of=$YOUR_MBR_DEVICE bs=512 count=1

# dd if=/dev/zero of=/dev/sda bs=512 count=1
1+0 records in
1+0 records out
512 bytes (512 B) copied, 9.5923e-05 s, 5.3 MB/s

 
Mbr is cleared, good luck