  We present the mid-infrared (MIR) light curves (LC) of 10 superluminous
supernovae (SLSNe) at $z<0.12$ based on WISE data at 3.4 and 4.6 $\mu$m. Three
of them, including PS15br, SN 2017ens, and SN 2017err show rebrightening which
started at 200--400 days and ended at 600--1000 days, indicating the presence
of dust. In four of the left seven SLSNe, dust emission was detected with
monochromatic luminosities of $10^7\sim10^8\ L_\odot$ at epochs of 100--500
days based on MIR colors $W1-W2\sim1$. Among the three SLSNe which show
rebrightening, we further analysed PS15br and SN 2017ens. We modeled the SEDs
at 500--700 days, which gives dust temperatures of 600--1100 K, dust masses of
$\gtrsim 10^{-2}\ M_\odot$, and luminosities of $10^8\sim10^9$ $L_\odot$.
Considering the time delay and the huge amount of energy released, the emitting
dust can hardly be pre-existing dust heated whether collisionally by shocks or
radiatively by peak SLSN luminosity or shock emission. Instead, it can be newly
formed dust additionally heated by the interaction of circum-stellar medium,
indicated by features in their spectra and slowly declining bolometric LCs. The
dust masses appear to be ten times greater than those formed in normal
core-collapse supernovae at similar epochs. Combining with the analysis of SN
2018bsz by Chen et al. (2022), we suggest that SLSNe have higher dust formation
efficiency, although future observations are required to reach a final
conclusion.
