Not at all, unless you respect a few advices.

A land with a certain state of poverty and hunger accordingly also provides a certain state of crime. In the US, many poor people get support from the state. So most of the felonies occur because of drugs, avarice or personal conflicts. In a land with a social class that has a monthly income resembling an average telephone bill of a US family, crime displays another motivation. Many poor and less educated people are looking for work, especially in the big cities. Hence precaution is recommended in certain districts. Do not reveal or exhibit your valuables and avoid nightly trips through dubious districts. Act with the known caution and reason at bus terminals, cab stations, mall exits etc. Costa Rica is the land with the lowest crime rate of Central America. Nevertheless you will find a lot of barred houses in the big cities. Intrusion and thievery needs prevention. Leaving the cities, you will find lesser measures of safety, larger properties and lower fences. Private condominiums give you the opportunity to reside in the city without fences or iron bars.

Conclusion: Costa Rica is NOT a dangerous place, unless you act with caution and mind.