In　Cognitive　Radio　(CR)　networks,　there　could　be　a　spectrum　market　which　operates　in　real　time　with　primary　users　(PU)　as　manager,　where　the　secondary　users　(SU)　pay　the　PUs　for　spectrum　resource　usage.　Multi-carrier　systems　such　as　OFDM　are　best　candidates　for　applying　in　CR　networks　because　of　the　spectrum　shaping　and　high　adaptive　capabilities.　In　this　paper,　an　optimal　resource　allocation　scheme　aims　at　maximizing　PU＇s　reward　in　OFDM-based　CR　networks　is　proposed.　Both　the　interference　limit　and　BER　requirements　of　SUs　are　considered　by　the　PU　to　allocate　its　spectrum　resources.　The　scheme　is　modeled　as　restless　bandits　problem,　which　can　dramatically　simplify　the　computation　and　implementation.　Furthermore,　extensive　simulation　results　show　that　our　proposed　scheme　can　improve　the　reward　of　PU　significantly　compared　to　the　existing　random　scheme　and　greedy　scheme.