c. 2000 in gamer slang, variant of newbie; often used interchangeably with it, but also often with a more derogatory shade of meaning; newbies owe their clueless behavior to lack of experience and are capable of improvement, while the fundamental characteristic of noobs is incorrigible obnoxiousness or stupidity.
"newcomer, new person to an existing situation," by 1969, from new with diminutive or derogatory suffix. Perhaps originally U.S. military slang. Compare noob. Middle English had newing "a new thing" (early 15c.); new was used as a noun meaning "naval cadet during first training on a ship" (1909); and newie "new thing" is recorded from 1946.