Seeking a permanent job during a postdoc in a different country/continent: official and moral responsibilities
Postdoc advisers understand that postdocs are temporary, and that their goal is to find a permanent position. If such a position comes along -- at times we cannot always predict -- then we're generally happy for our postdocs. At least that's the case for me.

In other words, I think it's ok if you mention that you are looking for jobs and may send out applications soon. You may want to re-assure your adviser that you have every intention to continue working on the project you're on until some position can be found, as well as finish any of the work you started even if you move somewhere else. It's a waste of an adviser's resources to pay someone for work that ultimately never gets finished, but it's an entirely different thing to pay someone for 6 months who will finish up the experiments, proofs, theorems, or the writing started earlier after they moved. In that case, as an adviser, I really only paid for 6 months, but get all of the work.