This paper proposes a new location-awareness system, ALTAIR (Automatic Location Tracking system with Active IR-tag) that automatically detects and tracks the locations of the mobile PC (Personal Computer) users. IR(InfraRed)-tag is stably detected and distinguished from the scenery by IR filtering camera. Combination of the IR-tag and wireless LAN (Local Area Network) enables ALTAIR to control the timing and the lighting pattern of the IR-tags through the network to perform stable tracking for multiple users. To identify the user and the location, detected IR-tag position and its network information (e.g. IP address) are associated with each other. ALTAIR is capable of dynamic management of the users' entry and automatically starts to aware the user's position when he/she enters the system area, using DHCP (Dynamic Host Configuration Protocol) performances. Our experimental results show the effective performance in terms of precision and stability for tracking and identifying the users' positions in an office environment.