Jay Adams seems to suggest that it is—unless, of course, you're bowing down to a piece of stone. At the very least, he's arguing that we're acting unbiblically if we help people identify their heart idols. Adams' comments are rather vague. It's not at all clear what he's responding to, or whether his preference is that counselors deal exclusively with raw human behavior rather than the affections that motivate the behavior.
Frankly, his comments are puzzling, since I'd assume most pastors and counselors would find some benefit in identifying the sinful heart issue beneath the sinful behavior. And it's not as if Adams (a Presbyterian) is coming from some hyper-dispensationalist position that radically bifurcates the OT prevalence of idolatry from the NT.
Adams, and all of us, ought to be able to recognize that the issue in OT idolatry isn't the nature of the object, but that the idol displaces God in the human heart. OT idolatry is a worship issue. It's about misplaced or distorted affections, values, allegiances, and hopes. One might well ask a NT sinning saint, "What were you loving or trusting in most at the moment you chose to sin? What lie were you believing about whom is worthy of your ultimate affections? What or whom were you really worshiping?" If that sort of communication isn't present in our preaching and our counseling, I'm not sure how we're going to accomplish anything more than behavior modification—treating symptoms
Of course, these notions aren't original with me. You can find them in Paul Tripp's books (especially this one), Tim Keller's sermons, and this outstanding little sermon series from Kevin Bauder. As I remember, the final sermon, "Shaping Our Affections Toward God" [MP3], spelled it out most directly.
Finally, and briefly, if you want NT texts that prove believers need to be warned about idolatry, in Galatians 5:19-20 one of the works of the flesh is idolatry. And even more explicitly, in Colossians 3:5 covetousness is idolatry. Covetousness—by definition a sin of the mind and heart.