Only once, but I don't use frogs too often.

I was watching a Dave Mercer Facts of fishing episode on You Tube where he had the same thing happen. A frog ate his frog lure. He was wondering if the frog was hungry or frisky.

Yes, just recently while shore fishing.  This guy was very aggressive - just wanted to destroy the lure.

Catching frogs on frog lures is very easy. They're aggressive and dumb as a post. I've caught them on purpose, released them, then caught them again with the same bait right after being released. 

We used to target them with a grub on a aberdeen hook at ponds to get frog legs. It's a fun and easy way to catch them. 

First time I fished a frog was on some moss beds at a tiny local pond that was full of frogs.  First cast as I was bringing back a huge toad decided to follow my frog as I hopped it along the surface.  Didn't let him catch it and eat it because I didn't want to hold/unhook it but it was definitely stalking the bait.

Sometimes I'll ride my bike down the road to a canal and fish for frogs. Once you find them, you will soon realize they will eat anything, including bare hooks. They usually aren't hard to find.