Earlier, they were forced to change their press conference venue following a late cancellation by the Marriott Hotel, in Dyce, allegedly following threats by a group called the Aberdeen Anti-Fascist Alliance.
Ukip president in Scotland Lord Christopher Monckton said there is a problem with democracy in Scotland, a place where only "the party line" is permitted.
This latest visit comes a month after Mr Farage was hounded out of a pub by protesters during an earlier campaign trip to Edinburgh on 16 May.
The by-election takes place on Thursday. The seat was made vacant by the death of SNP MSP Brian Adam. Mr Farage said: "It was very sweet of (Ms Boulton) to ask me but obviously there has been a lot of pressure brought to bear.
"There is this narrative, and we saw it in Edinburgh a month ago, and I also saw it on Question Time last week not just from the SNP but from a very senior journalist, saying that Ukip's voice shouldn't be heard here."So every attempt is being made to stop us from speaking.
"I've never come across anything like it in all of my life anywhere in Britain, Europe or the world for that matter.
"The idea that you can disagree with someone's point of view but you have it out and debate these things and let the public judge is what the democratic process is all about.
"There is something quite unpleasant going on. Huffington Post.
