Is that normal to have larger render time with GPU? I am using Blender 2.79 on Ubuntu 16.04.2. I have gtx610M(closed source drivers installed) and Intel(R) Core(TM) i5-3210M CPU  2.50GHz processor

I have a very simple scene. A cube placed on a plane.


I've rendered this scene with 128 samples. 32x32 tiles. With CPU I got it rendered in 25.56 seconds. But when I switch it to GPU I get it rendered in 1 minutes and 7 seconds. I tried increasing the tile size to 256x256 and then I got it in 54 seconds. 

Can that be natural? 1 minutes of GPU rendering time for this scene is obviously larger than normal, how about the CPU? Is 25 seconds ideal?
GPU's are generally a better solution for your renderings. They offer more processing power and that can be harnessed to render your scenes. 
Here your GPU might not be supported or your drivers not in place, If its not any of these, then its your GPU that is and. Get a newer one and it should work :)