“Christians have a bias.” If what you mean is that Christians have a bias in that they have a point of view, the answer is yes they do have a bias; but scientists have a bias in that sense too— scientists have a point of view.
But here’s something that’s important to keep in mind, and I owe this insight to Dr. J. P. Moreland. The Christian’s bias informs the process in a different way than a naturalistic scientist’s bias. A naturalist’s bias causes him to reduce the amount of options that he can consider; the Christian’s bias expands the options. So the Christian is capable of looking at the evidence and following the evidence wherever it leads. [For example,] you hear thunder, is that a natural thing or is that God’s voice? I don’t know, let’s look at the evidence; I’m open to either one depending on what the evidence says.
So in this sense, the Christian’s bias is a good thing because it increases the chances of learning the truth.
— Greg Koukl, from the Science and Faith, part 2 lecture at 20:10