Christie said months ago that, despite his personal opposition, he wasn't sure whether the government should legislate the therapy.
"I still have those concerns," he plans to say Monday. "Government should tread carefully into this area, and I do so here reluctantly. I have scrutinized this piece of legislation with that concern in mind."
But, Christie will note, the American Psychological Association has said that gay conversion therapy -- also known as reparative therapy -- can lead to mental health issues and substance abuse.
"I believe that exposing children to these health risks without clear evidence of benefits that outweigh these serious risks is not appropriate," Christie will say. "Based upon this analysis, I sign this bill into law."
Gay conversion therapy is a controversial practice. It became an issue in the 2012 presidential race when gay rights groups accused Marcus Bachmann -- the husband of Rep. Michele Bachmann's (Minn.), a GOP candidate -- of trying to convert gay people at a counseling center he owned. Marcus Bachmann denied that he was involved in such therapy.
California is the only state that has attempted a ban on gay conversion therapy but in December 2012 a three-judge panel of a U.S. appeals court blocked the ban, which was scheduled to take effect on January 1, 2013. Since then, no other states have enacted similar legislation.
Democrats criticized Christie for vetoing the gun bill. The governor had expressed support for banning the Barrett .50 caliber long-range rifle after the massacre in Newtown, Conn., but he said Friday that the measure would have gone too far by requiring owners of the weapon to forfeit it.
By contrast, his decision to sign the bill banning gay conversion therapy could alienate some Christian conservatives who believe that being gay is a choice and a sin.
Christie has charted a somewhat moderate course when it comes to gay rights issues. Although he vetoed a bill last year that would have legalized same-sex marriage, he favors civil unions and has said that he thinks people are born gay and that being gay is not a sin.