Is cosmic background radiation hot?
Actually, the word "hot" is not a very good term to use for a scientific description because it is pretty vague. It would be better to ask a more specific question about the temperature. A hot cup of coffee might be much cooler than the surface of a hot stove.
But in this case, the word "hot" would be considered to be the wrong answer for almost all comparisons. The cosmic background radiation has an average temperature of 2.7 Kelvin; just a few degrees above absolute zero. That's very cold by most standards.