  e present measurements on $D^0$ meson production via direct reconstruction of
its hadronic decay channel $D^0\to K\pi$ in minimum bias $d$+Au and Au+Au
collisions at $\sqrt{s_{NN}}$=200 GeV with $p_T$ up to $\sim$3 GeV/$c$.
Non-photonic electron spectra from the charm semi-leptonic decays are analyzed
from the same data set as well as in $p$+$p$ collision at $\sqrt{s}$=200 GeV
using the STAR Time-of-Flight (TOF) and Barrel EMC (BEMC) detectors,
respectively. Results of the charm-decayed single muon (prompt muon) spectra
are also presented at low $p_T$ in Au+Au collisions measured by the TOF
detector. The charm production total cross-section per nucleon-nucleon
collision is measured to be 1.26$\pm$0.09(stat.)$\pm$0.23(sys.) mb in minimum
bias Au+Au collisions, which is consistent with the $N_{bin}$ scaling compared
to 1.4$\pm0.2\pm$0.4 mb in minimum bias $d$+Au collisions, and supports the
idea that charm quarks should be produced mostly via parton fusion at early
stage in relativistic heavy-ion collisions. A Blast-Wave model fit to the low
$p_T$ ($<2$ GeV/c) non-photonic electrons, prompt muons and $D^0$ spectra shows
that charm hadrons may kinetically freeze-out earlier than light hadrons with a
smaller collective velocity. The nuclear modification factors ($R_{AA}$) of the
non-photonic electrons in central Au+Au collisions are significantly below
unity at $p_T>\sim$2 GeV/$c$, which indicates a significant amount of energy
loss for heavy quarks in Au+Au collisions. The charm transverse momentum
distribution must have been modified by the hot and dense matter created in
central Au+Au collisions at RHIC.
