Problem with Anti lock brakes engaging all the time during normal braking?

I have a 2002 chevy cavalier, has some electrical problems, service light and abs light come on whenever it rains, or snows...never had an issue with the brakes. lately the abs system has been engaging whenever i tried to brake, not at a fast speed, normal braking works fine until almost stopping, then the abs kicks in, causing car to slide at least once or twice. not sure what the deal is, not an expert with vehicles!.