Quite possibly. The A6-5400K is a weak CPU. It's better suited for laptops or Home theater PCs for your living room when you need everything integrated and good energy saving. They do a great job for that.
But for gaming, when you want to pair it with a more powerful card it's not really a good combo. If you want to stay in the AMD family, the FX series of CPU would have been better suited. Like the FX-6300 is a good bang for the bucks right now and an excellent gaming CPU that should be at least 3 times faster than your A6-5400K.
Another way to tell if the CPU is the bottleneck, monitor your components usage during gaming. If the CPU is at 100% all the time, and the GPU is only at 30% or 40% for example. It's a good indication you...