The anime was based on the novel that came out in 2001 which spawned a manga series as well.
Plot concept: Based on the popular Japanese novel by Tatsuhiko Takimoto (Negative Happy Chainsaw Edge) and its subsequent manga adaptation written by Takimoto and illustrated by Kendi Oiwa (Goth; Tsukumo Happy Soul), Welcome To The N.H.K. is a 24- episode anime series produced by Gonzo and directed by Yusuke Yamamoto (Aquarion Evol; Sakura Taisen: Le Nouveau Paris).
Now, it looks like a sequel novel is coming from Tatsuhiko Takimoto is on the way simply as New Welcome to the N-H-K.
One of the more amusing shows from a long time ago in an anime industry far, far, away, was the Welcome to the N-H-K anime series.