I am new to blender and have been following Blender Guru's beginner tutorial series. I just finished my coffee cup and went to render it and it does not show up, but it will show up in the rendered tab.
Your cup influencing plane, but is not visible.
Check your render layer settings:
On the left - all active layers
On the right - active layers for "RenderLayer" named render layer. You have one of them (with cup) switched OFF. That's why cup influence scene, but is not visible.