The Rema (OC 559:10) says that there is a Minhag to go straight after davening to the Bais HaKvaros on Tisha B'Av. The Mogen Avrohom brings from the Arizal that one should never go to a Bais Kvaros unless it is for a Levaya. The reason is because there are bad spirits in the cemetery. The Mishna Brura says that based on this Mogen Avrohom, on Tisha B'Av one should go near the cemetery to fulfill the minhag but not into the cemetery in accordance with the Arizal.
The Nimukei Orach Chaim says that the Mogen Avrohom only concerns himself with the Arizal by Hilchos Tisha B'Av since Tisha B'Av is a time when bad spirits have the upper hand. The Taamei Minhagim says that Tisha B'Av is a particular danger because we do not learn Torah and therefore are more vulnerable. In fact many are noheg not to go at all.
The Piskei Tshuvos brings that the Chazon Ish would go to the cemetery on Tisha B'Av. Some years he would go in between the graves and other years he would stay by the entrance without going in. The Steipler Gaon on the other hand would never go in, and in his later years would not even go to the Bais HaKvaros at all, not on Tisha B'Av nor any other time of year.