Yes, sometimes the door seals are to blame. Check them visually. If you find an area that looks suspect (or you want to check), then turn a on flashlight and put it inside pointed out toward the seal area. Turn off the lights in the room. If you can see light from the flashlight coming out of the refrigerator, you need to replace the gasket.
You should also be sure that the all the coils are clean and free of dust and greasy. They need good air flow to do their job correctly.
You can also check to see if the fan is blowing cold air from the freezer into the refrigerator as it should. Push the door switch in to "trick" the refrigerator into thinking the door is closed. You should hear a fan inside the unit that blows air from the freezer into the refrigerator.
Let me know what you find and we can give you a better answer.
We also need the model number of the refrigerator (usually found on the inside of the fresh food area on a wall).
How old is the refrigerator?