1. Check if the bands you are seeing in your negative control are specific to your experimental conditions. If not, then you may need to tweak the conditions (e.g. antibody concentration, blocking buffer, time of incubation) to reduce background staining.

2. Perform a titration experiment to determine the optimal antibody concentration.

3. Consider using an alternate blocking buffer or diluent, such as BSA, to reduce non-specific binding.

4. Check the specificity of your primary antibody by performing a Western blot with a positive control.

5. Consider using multiple antibodies targeting different epitopes of the protein of interest to increase specificity.

6. Consider using a different method to detect p-ERK, such as an ELISA or flow cytometry.