It's possible the speck is on the rear element of the lens. I would check that first, but it is most likely a spot on the sensor. Actually the low-pass filter in front of the sensor, but you probably know what I mean.
I think others have given you the advise to try a Rocket Blower, that would be a good idea. Don't use any other device to try blowing it out.
If that doesn't work, you will need a wet cleaning. It's fairly easy to DIY, see the site - they have the best system going. But if you feel uncomfortable (quite understandable), a good local camera shop could do the job for you. I would not recommend sending it to Nikon for this, unless you have some other problem you would want them to look at as well. Too expensive, and I've heard stories about the camera coming back with the same or more spots than when it went to them.
Good luck, and for now you should be able to post-process the images as needed.