I agree with Laura. Frustration is a normal part of the learning process. So, unless you've truly lost interest in dancing, I'd say, don't quit!
It might help if you could pinpoint the cause of your frustration. There are probably some specific problems that are "infecting" your whole feeling about dance. I don't know how long you've been dancing or what your goals are, but here are some ideas:
My teacher told me that there are three parts to the learning process that get replayed over and over as you progress. When you start learning something new or are beginning to take your dancing to a new level, it's difficult and frustrating and you can feel like you're dancing worse that you were before. Then, you "get it" and can do it well as long as you focus and concentrate. Finally, it becomes a natural part of your dancing. So you move on to a new level and start the three-step process all over again.
So your frustration might be a good sign if it means that you're starting to take your dancing to a new level. In that case, just live with it, practice more, and have faith that it will pass as you progress. (I find looking at past tapes of my dancing helps me realize how far I've come.)
But if you're at the plateau stage, and you feel like you're just continuing to dance at the same level without progressing, maybe you need more of a challenge, to learn something new and advance your technique in specific ways.
Also, are your goals very long-term, like to win a comp at a level that's realistically several years away? That's great. (I joke with my instructor that I have my eye on a national championship in the over-80 age group 'cuz it will take me that long to get there!) But it can be frustrating to work toward a goal that's too far away, so it can help to break it down into interim goals. What do you want to accomplish in the next six months? What do you need to do to get there? What do you want to accomplish in your next lesson?
To perk up your enthusiasm (and also get some additional help), you might ask your coach to refer you for a one-time lesson to an advanced professional s/he admires. That person could assess your dancing and advise you on what to address next to get you toward your goals. Or attend a dance camp, if you can. You'll be exposed to lots of different kinds of dancing and different teachers and have a great time, too!
Good luck! Let us know how things work out.