If this mead has been going for a few days already, the DO NOT add oxygen. You will most likely ruin your brew. Mead takes a while to ferment, and if you had some initial fermenting, then it probably had "enough" oxygen. Not an idea amount maybe, but it is too late to worry about that.
If you want to help it out, you could try giving it a gentle stir to see if CO2 is released. This can lower the pH of the must and slow things down, or even stop the process. You should also make sure that the brew is warm enough, but not too warm. Each yeast has it's own ideal fermentation temperatures. A quick google search should get you that info. If it is too cold, things will slow down or stop.
Forget about adding oxygen for this batch, but try to remember it for the next one.
The only exception would be if your brew really hasn't dropped below the 3/4 sugar break yet (I personally try to keep oxygen out shortly before the 1/2 sugar break). If you have your OG and SG reading we can confirm that this isn't the case.