Abstract: A baseline can be defined using specific attributes of the network traffic. Using the established baseline, deviation can then be measured to detect anomaly on the network. The accuracy of the baseline is the most important criterion of any effective network anomaly detection technique. In a local area network (LAN) environment, the attributes change very frequently by many change agents; for example, new entities, such as users, application, and network-enabled devices, added to and removed from the LAN environment. The invention provides an improved method of establishing a baseline for network anomaly detection based on user's behaviour profiling. A user behaviour profiling is a distinct network usage pattern pertaining to a specific individual user operating on the LAN environment. No two users profiling would be the same. A group of users that have similar network usage attributes can be extrapolated using data mining technique to establish a group profiling baseline to detect network usage anomaly.