Existing powderpost beetle infestations are very difficult to control because the larvae are buried inside the wood for the majority of their lives (1 - several years). The best option is often to do nothing unless the infested wood is very valuable. Older wood is less likely to be re-infested by emerging beetles so the chances of new damage is less, but not zero. The only effective treatment is whole house fumigation which can be extremely expensive. In some cases infested wood such as wood floors will be damaged to the point of replacement but often the infestation just "burns itself out".  Since you are not seeing sawdust the holes may be old.  The picture isn't clear enough to give a positive id but it may be one of the grain beetles, if this is the case they are only looking for a home and vacuuming would take care of the problem. See
http://www.extension.umn.edu/garden/diagnose/insect/indoor/beetles/small/ for more information.