Depending on what the keyboard is, it's probably just dirty or something got spilled on it. Common enough and simple enough to solve.

If it's a peripheral keyboard, it really isn't hard to clean them. lay a paper towel on your desk, flip the keyboard over and give it a few hard taps on the back to shake out the grim. Then you can take the keyboard apart by using a flat bladed screwdriver or mini pry bar to lever the keys off. Do the same again with the towel and tapping method. Using a cotton bud & Isopropyl Alcohol (most electronic stores will stock this as "cleaning fluid"). Then cleaning in between the key-spots and clean the keys themselves. I recommend taking a photograph of the keyboard first so you know where all the keys go, because to get the best results, you need to remove the keys and clean underneath them where the grime gets.