Herschel images in six photometric bands show the thermal emission of the debris disk surrounding β Pic. In the three PACS bands at 70 μm, 100 μm and 160 μm and in the 250 μm SPIRE band, the disk is well-resolved, and additional photometry is available in the SPIRE bands at 350 μm and 500 μm, where the disk is only marginally resolved. The SPIRE maps reveal a blob to the southwest of β Pic, coinciding with submillimetre detection of excess emission in the disk. We investigated the nature of this blob. Our comparison of the colours, spectral energy distribution and size of the blob, the disk and the background sources shows that the blob is most likely a background source with a redshift between z = 1.0 and z = 1.6.