The role of Intrusion Detection System (IDS) has been inevitable in the area of Information and Network security – especially for building a good network defense infrastructure. Due to the wide popularity of wireless networks tremendous applications are emerging and Wireless Local Area Network (WLAN) has gained attention by both research and industry communities. The wide spread deployment of WLAN has also brought new challenges to security and privacy. The authors need to distinguish anomalies that change the traffic either abruptly or slowly. Anomaly based intrusion detection technique is one of the building blocks of such a foundation.