There are any number of things that cause ping fluctuations. Signal Interference, Software, Drivers, Hardware, Power Irregularities, Misconfigured Firewall, Load balancing.
The best way to see if it is a software issue is to format and run the test again without installing any other software. Hardware is a little more difficult, power irregularities can be resolved by getting an uninterruptible power supply, signal interference can be adjusted at the router normally, and ensure you have the latest drivers for your wireless adapter in your PC.
See my post: http://www.tomshardware.com/faq/id-1725173/troubleshooting-wireless-ping-fluctuations.html