Hi there,
Sorry to hear your big guy is having troubles.
It sounds like he may be have a localized seizure. Seizures in cats can manifest in different ways, not just the body convulsions we associate with a seizure. They can blink their eyes rapidly and franticly, a limb can become stiff, all seizures. Because he is a maine coon kitty it would be a good idea to get his heart evaluated just to be sure it isn't playing a role. If you've had many maine coons you know they can be predisposed to heart conditions, more so then other breeds.
If you only noticed this once, watch him closely for more. If they become more frequent get him in to your vet. If you notice anything else, rapid breathing, weight loss, not eating well, ect, also get him in.
It is also possible that his arm is painful and the twitching you see is a response to pain. Well he let you move the limb with no complaints? Does he have a hard time jumping up or down? As he ages, he can develop arthritis. There is a kitty supplement of cosiquine called dasiquin that is a flavored powder you add to his food. It also has some fatty acids in it, and has no side effects. You can ask your vet, or check out an online pharmacy for the product.
Hope this helps and let me know if you have any other questions. Also here is an article about the heart condition maine coons seem to be prone to, so you know what to look for. http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=2507
Carrie, Cvt
Certified Veterinary Technician
I've been a Vet tech for 9 yr, cats only since '05. I am a member of Amer. Asoc. feline practioners