The economic climate indicator, which measures business confidence, stood at plus 0.5 in November, down from 0.7 the previous month, which was its highest level since July 2008. The index turned positive in May - the month Lisbon exited its international bailout.
The National Statistics Insititute also said its consumer confidence indicator rose to a negative reading of 22.3 this month, from minus 24.0 in October.
The indices started rebounding at the start of 2013, when Portugal began to recover from its debt crisis which led to the worst economic slump since the 1970s. This year, the economy is expected to grow for the first time since 2010.