Mr Walker is accused of racial intolerance
A British National Party activist posted racist comments online while working as a teacher in County Durham, a disciplinary panel heard.
The General Teaching Council (GTC) was told Adam Walker used a school laptop to post descriptions of some immigrants as "savage animals" and "filth".
Mr Walker, from Spennymoor, said he had been singled out because of his views.
About 60 BNP and Unite Against Facism (UAF) members protested outside the hearing in Birmingham on Monday.
Mr Walker is the first teacher to appear before the GTC accused of racial intolerance. It is alleged that the views expressed in the postings constitute unacceptable professional conduct.
He resigned from Houghton Kepier Sports College, in Houghton-le-Spring, in 2007 after his headteacher asked IT staff to investigate his use of the internet.
Before the hearing, Mr Walker said: "Unfortunately if you want someone to lose their job in this day and age all you need to do is crawl through their computer.
"I'd be the first teacher in British history who could lose their job because of what they think."
GTC presenting officer Bradley Albuery told the hearing that postings made by the teacher demonstrated views suggestive of both "racial" and "religious" intolerance.
The panel heard he used a school laptop to access an online forum - Teessideonline - which addressed the popularity of the BNP, throughout February and March 2007.
In one posting, it was alleged Mr Walker claimed the BNP had risen in popularity because "they are the only party who are making a stand and are prepared to protect the rights of citizens against the savage animals New Labour and Bliar (sic) are filling our communities with".
The hearing was told that in another posting on the same day, Mr Walker wrote: "By following recent media coverage of illegal animals and how they are allowed to stay here despite committing heinous crimes, I am, to say the very least, disgusted."
Another posting claimed that some immigrants hated people who were white and had western values, the panel heard.
Mr Albuery said: "This case is about the actions and behaviour of a registered teacher, using school property on school premises in school time."
The teacher's trade union representative, Patrick Harrington, told the panel that Mr Walker accepted he was wrong to use a computer to access the online forum during school time.
However, he argued that none of the terms used by Mr Walker had demonstrated racial or religious intolerance.
He said: "Immigrant is not a racial term. Immigrant is simply a description of people moving to one country from another country - immigrants comprise of all different races."
"There is an underlying prejudice and assumption that he is thinking in a racial way."
The hearing was adjourned and a judgement will be announced on Tuesday.