Abstract：We report observations of a transient Fermi J1544-0649 from radio to gamma-rays. Fermi J1544-0649 was discovered by the Fermi/LAT in May 2017. Follow-up Swift/XRT observations revealed three flaring episodes. Optical spectral measurements taken by the Magellan 6.5-m telescope and the Lick/Shane telescope both show a largely featureless spectrum, strengthening the BL Lac interpretation first proposed by Bruni et al. (2018). However, in the Li-Jiang spectrum we found a broad absorption line (BAL) feature, which is a sign of mis-alignment of the jet with the line of sight. The weekly time-scale variation of the optical magnitude does not follow those seen at high energies. Our RATAN-600m measurements at 4.8~GHz and 8.2~GHz indicate a steady radio flux which is consistent with the NVSS level. The optical and radio emission should then come from regions that are not responsible for the large variation seen at high energies. During GeV flaring times, the spectrum is very hard (index~1.7) in the GeV band and at times also very hard (\Gamma_X~<2) in the X-rays, similar to a high-synchrotron-peak (or even an extreme) BL Lac object, making Fermi J1544-0649 a good target for ground-based Cherenkov telescopes. Fermi J1544-0649 may be a mis-aligned blazar. Future VLBI observations are crucial to probe this.