Some things have a dim view of being dimmed
Things other than lamps, such as motors and some electronic loads, often take a rather dim view of being connected to a dimmed receptacle. This may range from merely "not working" to "overheating and catching on fire", something you (and the NFPA) would rather not have happen. So, the 2014 NEC prohibits your current configuration in 406.15:
406.15 Dimmer-Controlled Receptacles. A receptacle supplying lighting loads shall not be connected to a dimmer
unless the plug/receptacle combination is a nonstandard
configuration type that is specifically listed and identified
for each such unique combination.
This leaves you with two options -- either you can swap the culprit dimmer out for a switch, or you can use a special receptacle and plug to prevent non-lamps from being plugged in to the dimmed outlet.
Swapping a dimmer for a switch is a relatively easy task, at least as far as single pole configurations are concerned:
- Turn the power to the circuit off at the breaker
- Remove the old dimmer + faceplate from the box and undo the terminal screws
- Connect the new switch's brass screws to the two wires that went to the dimmer's brass screws (they may be any color but green or bare). Which wire goes to which brass terminal doesn't matter, either.
- Connect any bare or green wire present to the new switch's green grounding screw.
- Put the switch back in the box and put the faceplate back on
- Turn the circuit back on
Keeping pesky non-lamps at bay
Lutron makes a plug and receptacle combination for this job -- the receptacle you need is a Lutron HDTR, and you'll have to put the matching plug on whatever lamp you plug into the dimmed receptacle, as well.
This is the costlier and slightly trickier option of the two, but may be needed if the dimmer serves other lights as well as the half-dimmed receptacle or otherwise can't be removed.