Absol rarely are forthcoming, but take a good look at its body language to be sure.
If it looks concerned, worried, or deadly serious, keep an eye out for further activity. The more agitated it seems, the closer to disaster you are. Pay attention to it if it begins to bark or if it runs at you. You see, absol predict disaster; they don’t bring it. As such, when they appear before humans, what they’re actually doing is making an active attempt to warn or protect us. Thus, in a way, this absol may be keeping an eye on you because it knows there may be disaster in your future, but it’s not immediate. It will, however, take action and do everything it can to warn you away from danger if it senses that the threat is very close at hand. (Unless of course it’s a particularly sadistic absol … at which point keep an eye out for any excited behavior anyway.)
If, however, it looks relaxed, it simply feels that your yard is a safe place to sit, or it found a food source somewhere close to where you live. You may consider approaching it and offering to train it in this case (and if you do, be aware that you’re dealing with a wild pokémon and thus should do so cautiously), but otherwise, it’s really nothing to be concerned about.