You give one example of the type of question you ask. Are all your questions of an academic nature, or other things as well, like "What would you like to do now?" or "Will you help me find your red sweater?"
If you're asking for academic answers, then I'd say he is genuinely anxious about giving you the right answer, because (1) there is generally only one right answer, (2) he's a little young to have all those facts, letters, numbers, shapes, etc. sorted out and easily accessible, and (3) you apparently get frustrated if he doesn't get to the answer in time.
He's got a couple of years yet to start nailing down his ABC's and 123's. And some kids need more time for those activities – it's a matter of the development of various brain regions, which vary quite a bit from one child to another. Until then, keep whatever education you offer playful and light, so that he doesn't develop an aversion to academic learning.
For the next couple of years the best educational support you can give him is to encourage imaginative play that incorporates lots of language. A large vocabulary is the single best predictor of a child's success in school. He will develop a love of reading and arithmetic if you enjoy reading yourself and read with and to him often, and if you find games that incorporate the use of numbers and counting.