A portable terminal for providing a Wi-Fi Peer-to-Peer (P2P) function is provided. An apparatus and a method of a portable terminal for enhancing a data transmission performance by adjusting a Notice of Absence (NoA) duration in a NoA-based power saving mode are provided. The apparatus includes a communication unit for receiving Notice of Absence (NoA) information for a power saving mode, a control unit for controlling a client of a group to enter the power saving mode based on the NoA information, and a power management unit for generating the NoA information for the power saving mode.