Yes, it's likely a dust bunny! Welcome to the world of DSLR's. Agree that a blower can actually blow more dust into the sensor. The dust particle will not necessarily even be visible to the naked eye...been there...done that (search for my previous posts)! Could also be shutter lubricant, if so, blowing won't help anyway.... There are many cleaning methods with varying degrees of success out on the web...Send to Nikon, blowers, brushes, Pec Pads with Eclipse....even Scotch Tape! Go there at your own risk.....

In youth, we learn....with age, we understand.