The Bible does not explicitly forbid kissing between two unmarried people. A Christian couple who are dating with the intention of marriage or who are engaged may not necessarily be committing a sin if they share a kiss in a way that preserves their purity. This varies from one couple to another. Some Christians do not even hold hands until marriage, while others may kiss their boyfriend or girlfriend regularly.
The issue at hand is, once again, the heart of those involved. Are these acts of affection performed with a clear conscience before God? This does not mean that all kisses shared with a partner or someone we love are sinful. Most Christian denominations do not consider mutual affection between romantic partners to be sinful. However, it is important to be mindful of what is in our heart and make sure we maintain self-control when kissing.
If you plan to kiss more for pleasure than for being an act of pure love, then it can likely be considered a sin. Although it is not exactly kissing directly, this could be helpful in making a decision that works for you when dating as a Christian.