Scott Kelby, his book Photoshop CS for Digital Photographer, proposed following method
1. Load the image file
2. Change the image color mode to to Lab color thru Image>Mode>Lab Color
3. Now go to the Channels & select channel "a"
4. From menu, use Filter menu, under Blur, choose Gaussian Blur to blur out the noise
5. In Gaussian Blur dialog box, increase radius (i.e. amount of blur) until the dots disappears
6. Now select channel "b" & repeat step 5
7. Going back to the Image menu, use Image>Mode> RGB to return to RGB colour mode
8. The noise level should have improved