If there was a problem, you would probably know about it the first time you switched on the computer. There would be no remaining charge. The best option, as mentioned earlier, is to have a filter and sealed case to minimize the problem. The key points are to minimize touching components as much as possible to avoid static discharge, not getting dust in sockets, not getting any other gunk anywhere, and remembering that some parts are safer than others - the case itself and the power supply aren't going to be easily damaged, for example. The memory modules are among the most static sensitive parts, but as long as they are well seated they have some protection. Also, a portable vacuum, carefully used (don't touch anything you don't have to) probably isn't too dangerous. Wear an anti-static strap and, if you want to be really careful, wait for a humid day.

But honestly, a mobo can usually take quite a lot of abuse. I probably caused static damage to a memory module once, while replacing it, back in the early '90s. I've never done damage cleaning, and I give away, store, or sell old computers before they fail. I build my own computers (in as much as sticking parts in parts can be called "building" anyway).