I was going by their FAQ, which does currently read that it is currently airing. After further investigation EVERYWHERE but the the official website, I realize that this is correct, and I've sent a semi scathing albeit polite- not enough space to be otherwise- email to their Website Help page. I don't know if they'll read it but I know I'm furious.
I only looked for it because my parents are the Merlin fans- I'm a Doctor Who girl myself.
To see the error on the official page yourself, please refer to:
http://www.bbc.co.uk/merlin/faq/show
where it currently states(retrieval time 8:24pm EST):
"When is Merlin on TV? Merlin Series 4 is currently being shown on Saturday nights on BBC One and is repeated on BBC Three."
My understanding of the main page for the program is that they are airing episodes Saturday nights, but the 13 commissioned series 4 episodes have aired, so either they are airing repeats, or have not updates the page to reflect the end of series 4. I can assure you that the date of December 24 2011 for the finale is correct. Trut-h-urts man (talk) 01:37, 3 January 2012 (UTC)
I totally believe you. Thus the mentioning furious email to the BBC. Just explaining why I thought there was an error on the page.