The answer is not as simple as a yes or a no. There are many antibiotics that can perfectly safely coexist with a new pregnancy, but it is a good idea to read the package insert yourself when you are prescribed a course of antibiotics. Sometimes, a particular type of antibiotic will have an outright warning to pregnant women, those trying to conceive, and nursing mothers. Most antibiotics will just include a note that you will have to inform your doctor if you are trying to get pregnant. It is up to doctor then to decide whether antibiotics are safe for you or not. I strongly believe that antibiotics are overused in most of the western world. Most doctors would agree with that. If you follow medical news, you will notice statements from doctors associations saying that the use of antibiotics should be brought down, and that many medical practitioners are too quick to opt for antibiotics.
Depending on the reason you are being described antibiotics, if you are trying to conceive, it might be a good idea to ask if there are any non-antibiotic medications available for your condition. In the case of a urinary tract infection for instance, turning to Traditional Chinese Medicine, naturopathy, or homeopathy is a very valid alternative to using antibiotics. The same goes for many other conditions that are conventionally treated with antibiotics. Having said that, some conditions simply require the use of antibiotics, and in that case, you can discuss with your doctor whether it would be better to take a month off trying to get pregnant. Fortunately, on the whole, the answer to that question will be, "No, taking antibiotics will trying to conceive does not pose any risk".