In a network unauthorized access to a computer is more prevalent that involves a choice of malicious activities. Hence it is essential for a system to be aware of normal system activities. Data mining is the process of summarizing information from various perspectives. Confessing of sensitive information poses another security risk when large amount of interrelated data is processed. This is where intrusion detection plays a vital role in identifying the suspect. Several data mining approaches for intrusion detection have been proposed as a countermeasure and anomaly detection is one such technique.