A group key agreement protocol involves all participants cooperatively establishing a group key, which is used to encrypt/decrypt transmitted messages among participants over an open communication channel. Unfortunately, most previously proposed group key agreement protocols are too expensive computationally to be employed in mobile wireless networks with resource-limited mobile devices. Recently, two group key agreement protocols suitable for a mobile wireless network have been proposed. However, in this paper we demonstrate that two proposed protocols do not satisfy some important security properties of group key agreement such as forward secrecy and contributory key agreement.