An antistatic floor mat or ground mat is one of a number of antistatic devices designed to help eliminate static electricity. It does this by having a conductive material embedded within the mat that collects the static. The mat would need to be grounded (earthed). This is usually accomplished by plugging into the grounded line in an electrical outlet. It's important to discharge at a slow rate, therefore a resistor should be used in earthing the mat. Some ground mats allow you to connect an antistatic wrist strap to them.

Reference

• Webopedia
• Anti-Static Mat manufacture