Joint allocation of resources, namely subcarrier assignment and power profiles at the sources and relay nodes is considered for amplify and forward (AF) relaying scheme for two users using orthogonal frequency division multiple access (OFDMA). The objective is to allocate the resources to maximize the weighted sum rate subject to individual power constraint on each node. We formulate such a problem as subcarrier based resource allocation that seeks joint optimization of subcarrier assignment and power profiles at the source and relay nodes. Using high signal-to-noise-ratio (SNR) approximation, a low complexity algorithm is proposed to split the subcarriers into two partitions based on channel gains' ordering, where each partition is assigned to one user. The computational complexity of finding the subcarrier assignment that maximizes the weighted sum rate for N subcarriers AF-OFDMA scenario is of O(N). The merits of the proposed algorithm is demonstrated by numerical simulations.