The abbreviations i.e. (which means “that is” or “in other words”, from Latin id est) and e.g. (which means “for example”, from Latin exempli gratia) are always preceded by a punctuation mark, usually a comma or a bracket, as in
The CPU (i.e.[,] the processor) of your computer is overheating.
The question is, should a comma also follow the abbreviation? The answer is: It depends on whether you want to follow the American style or the British style.
In British English, “i.e.” and “e.g.” are not followed by a comma, so the first example above would be:
Virtually all American style guides recommend to follow both “i.e.” and “e.g.” with a comma (just like if “that is” and “for example” were used instead), so the very same sentence in American English would become:
Nevertheless, many American authors and bloggers are unaware of this recommendation, so you are much more likely to read a text with no commas after “i.e.” and “e.g.” written by an American than a text written by a British author with the commas included.