If you mean the various Dream Teams - then nope. Never have been beaten and probably won't for a long, long, time.
If you mean Pre-Dream Team then sure. A few times. One Olympics they were robbed by the refs and lost to the Russians. I think they've won silver and bronze other times as well.
You have to remember that pre-Dream Team the players were made up of College All Stars who were talented but not as skill developed or physically developed compared to other "men" playing for other countries. In addition, most other national teams had played together for quite awhile as opposed to US Oly teams made up of college players put together quickly and having very limited playing time with each other.